Józef Klemens Piłsudski (December 5, 1867 – May 12, 1935) was Chief of State (1918–22), "First Marshal" (from 1920) and (1926–35) the authoritarian leader of the Second Polish Republic. From mid-World War I he had a major influence in Poland's politics, and was an important figure on the European political scene. He is considered largely responsible for Poland's regaining its independence in 1918, after 123 years of partitions. Piłsudski was unable to incorporate much of his Lithuanian homeland to the newly resurrected Polish State.

Early in his political career, Piłsudski became a leader of the Polish Socialist Party. Concluding, however, that Poland's independence would have to be won by force of arms, he created the Polish Legions. In 1914 he anticipated the outbreak of a European war, the Russian Empire's defeat by the Central Powers, and the Central Powers' defeat by the western powers. When World War I broke out, he and his Legions fought alongside the Austro-Hungarian and German Empires to ensure Russia's defeat. In 1917, with Russia faring badly in the war, he withdrew his support from the Central Powers. From November 1918, when Poland regained independence, until 1922, Piłsudski was Poland's Chief of State. In 1919–21 he commanded Poland's forces in the Polish-Soviet War. In 1923, with the Polish government dominated by his opponents, particularly the National Democrats, he withdrew from active politics. Three years later he returned to power with the May 1926 coup d'état, and became the de facto dictator of Poland. From then until his death in 1935, he concerned himself primarily with military and foreign affairs. For at least thirty years until his death, Piłsudski pursued, with varying degrees of intensity, two complementary strategies, intended to enhance Poland's security: "Prometheism", which aimed at breaking up, successively, Imperial Russia and the Soviet Union into their constituent nations; and the creation of an Intermarum federation, comprising Poland and several of her neighbors. Though a number of his political acts remain controversial, Piłsudski's memory is held in high esteem by his compatriots.

Józef Piłsudski was born on December 5, 1867, at his family's manor in the village of Zalavas (Polish: Zułów), then part of the Russian Empire, currently part of the Švenčionys district municipality of Lithuania. The area had been part of the Grand Duchy of Lithuania, itself a component of the Polish-Lithuanian Commonwealth, before the latter had been partitioned by the Austrian Empire, the Russian Empire and the Kingdom of Prussia at the end of the 18th century. The Piłsudski family, impoverished szlachta, cherished Polish patriotic traditions and has been characterized either as Polish or as Polonized-Lithuanian. Young Józef was the second son born to the family. Józef, when he attended the Russian gymnasium at Vilnius, was not an especially diligent student. As an irony of history, one of the younger students at this gymnasium was the future communist Felix Dzerzhinsky, who later would become Piłsudski's archenemy. Along with his brothers Adam, Bronisław and Jan, Józef was introduced by his mother Maria, née Billewicz, to Polish history and literature, which were suppressed by the Russian authorities. His father, likewise named Józef, had fought in the January 1863 Uprising against Russian rule of Poland. The family resented the Russian government's Russification policies. Young Józef profoundly disliked having to attend Russian Orthodox Church service and left school with an aversion not only for the Russian Tsar and the Russian Empire, but for the culture, which he knew well.

In 1885 Piłsudski started medical studies at the Kharkiv University, where he became involved with Narodnaya Volya, part of the Russian Narodniki revolutionary movement. In 1886 he was suspended for participating in student demonstrations. He was rejected by the University of Dorpat (Tartu, Estonia), whose authorities had been informed of his political affiliation. On March 22, 1887, he was arrested by Tsarist authorities on a false charge of plotting with Vilnius socialists to assassinate Tsar Alexander III. In fact Piłsudski's main connection to the plot was the involvement in it of his elder brother, Bronisław. Bronisław was sentenced to fifteen years' hard labor (katorga) in eastern Siberia.

Józef received a milder sentence: five years' exile in Siberia, first at Kirensk on the Lena River, then at Tunka. While being transported in a prisoners' convoy to Siberia, Piłsudski was held for several weeks at a prison in Irkutsk. There he took part in what the authorities viewed as a revolt: after one of the inmates had insulted a guard and refused to apologize, he and other political prisoners were beaten by the guards for their defiance; Piłsudski lost two teeth and took part in a subsequent hunger strike until the authorities reinstated political prisoners' privileges that had been suspended after the incident. For his involvement, he was sentenced in 1888 to six months' imprisonment. He had to spend the first night of his incarceration in 40-degree-below-zero Siberian cold; this led to an illness that nearly killed him and to health problems that would plague him throughout life. During his years of exile in Siberia, Piłsudski met many Sybiraks, including Bronisław Szwarce, who had almost become a leader of the January 1863 Uprising. He was allowed to work in an occupation of his own choosing, and earned his living tutoring local children in mathematics and foreign languages (he knew French, German and Lithuanian in addition to Russian and his native Polish; he would later learn English). Local officials decided that as a Polish noble he was not entitled to the 10-ruble pension received by most other exiles.

In 1892 Piłsudski returned from exile and settled in Adomavas Manor near Teneniai (now in Šilalė district). In 1893 he joined the Polish Socialist Party (PPS) and helped organize its Lithuanian branch. Initially he sided with the Socialists' more radical wing, but despite the socialist movement's ostensible internationalism he remained a Polish nationalist. In 1894, as its chief editor, he began publishing an underground socialist newspaper, Robotnik (The Worker); he would also be one of its chief writers, and, initially, a typesetter. In 1895 he became a PPS leader, and took the position that doctrinal issues were of minor importance and that socialist ideology should be merged with nationalist ideology, since that combination offered the greatest chance of restoring Polish independence.

On July 15, 1899, while an underground organizer, Piłsudski married a fellow socialist organizer, Maria Juszkiewiczowa, née Koplewska. The marriage deteriorated when, several years later, Piłsudski began an affair with a younger socialist, Aleksandra Szczerbińska. Maria died in 1921, and in October that year Piłsudski married Aleksandra. By then the pair had two little daughters, Wanda and Jadwiga. This marriage, too, was troubled.

In February 1900, after Russian authorities found Robotnik's underground printing press in Łódź, Piłsudski was imprisoned at the Warsaw Citadel. But, after feigning mental illness in May 1901, he managed to escape from a mental hospital at Saint Petersburg with the help of a Polish physician, Władysław Mazurkiewicz, and others, fleeing to Galicia, then part of Austria-Hungary. At the time, when almost all parties in Russian Poland and Lithuania took a conciliatory position toward the Russian Empire and aimed at negotiating within it a limited autonomy for Poland, Piłsudski's PPS was the only political force that was prepared to fight the Empire for Polish independence and to resort to violence in order to achieve that goal.

On the outbreak of the Russo-Japanese War (1904 – 1905), in the summer of 1904, Piłsudski traveled to Tokyo, Japan, where he tried unsuccessfully to obtain that country's assistance for an uprising in Poland. He offered to supply Japan with intelligence in support of its war with Russia and proposed the creation of a Polish Legion from Poles, conscripted into the Russian Army, who had been captured by Japan. He also suggested a "Promethean" project directed at breaking up the Russian Empire — a goal that he later continued to pursue. Another notable Pole, Roman Dmowski, also traveled to Japan, where he argued against Piłsudski's plan, endeavoring to discourage the Japanese government from supporting at this time a Polish revolution which Dmowski felt would be doomed to failure. Dmowski, himself a Polish patriot, would remain Piłsudski's political arch-enemy to the end of Piłsudski's life. In the end, the Japanese offered Piłsudski much less than he had hoped for; he received Japan's help in purchasing weapons and ammunition for the PPS and its combat organisation, while the Japanese declined the Legion proposal.

In the fall of 1904, Piłsudski formed a paramilitary unit (the Combat Organization of the Polish Socialist Party, or bojówki) aiming to create an armed resistance movement against the Russian authorities. The PPS organized an increasing numbers of demonstrations, mainly in Warsaw; on October 28, 1904, Russian Cossack cavalry attacked a demonstration, and in reprisal, during a demonstration on November 13, Piłsudski's paramilitary opened fire on Russian police and military. Initially concentrating their attention on spies and informers, in March 1905 the paramilitary began using bombs to assassinate selected Russian police officers.

During the 1905 Russian Revolution, Piłsudski played a leading role in events in Congress Poland. In early 1905, he ordered the PPS to launch a general strike there; it involved some 400,000 workers and lasted two months until it was broken by the Russian authorities. In June 1905, Piłsudski sent paramilitary aid to an uprising in Łódź. During the "June Days", as the Łódź uprising came to be known, armed clashes broke out between Piłsudski's paramilitaries and gunmen loyal to Dmowski and his National Democrats. On December 22, 1905, Piłsudski called for all Polish workers to rise up; the call went largely unheeded.

Unlike the National Democrats, Piłsudski instructed the PPS to boycott the elections to the First Duma. This decision, and his resolve to try to win Polish independence through uprisings, caused tensions within the PPS, and in November 1906 the party fractured over Piłsudski's leadership. His faction came to be called the "Old Faction" or "Revolutionary Faction" ("Starzy" or "Frakcja Rewolucyjna"), while their opponents were known as the "Young Faction", "Moderate Faction" or "Left Wing" ("Młodzi", "Frakcja Umiarkowana", "Lewica"). The "Young" sympathized with the Social Democrats of the Kingdom of Poland and Lithuania and believed that priority should be given to cooperation with Russian revolutionaries in toppling the Tsarist regime and creating a socialist utopia that would facilitate negotiations for independence. Piłsudski and his supporters in the Revolutionary Faction continued to plot a revolution against Tsarist Russia that would secure Polish independence. By 1909 his faction would again be the majority in the PPS, and Piłsudski would remain one of the most important PPS leaders up to the outbreak of the First World War.

Piłsudski anticipated a coming European war and the need to organize the nucleus of a future Polish Army which could help win Poland's independence from the three empires that had partitioned her out of political existence in the late 18th century. In 1906, Piłsudski, with the connivance of Austrian authorities, founded a military school in Kraków for the training of paramilitary units. In 1906 alone, the 800-strong paramilitaries, operating in five-man teams in Congress Poland, killed 336 Russian officials; in subsequent years, the number of their casualties declined, while the paramilitaries' numbers increased to some 2,000 in 1908. The paramilitaries also held up Russian currency transports leaving Polish territories. On the night of September 26–27, 1908, they robbed a Russian mail train carrying tax revenues from Warsaw to Saint Petersburg. Piłsudski, who took part in this Bezdany raid near Vilnius, used the funds thus "expropriated" to finance his secret military organization. The take from that single raid (200,812 rubles) was a fortune for the time and equaled the paramilitaries' entire takes of the two preceding years. In 1908 Piłsudski transformed his paramilitary units into an "Association for Active Struggle" (Związek Walki Czynnej, or ZWC), headed by three of his associates, Władysław Sikorski, Marian Kukiel and Kazimierz Sosnkowski. One of the ZWC's main purposes was to train officers and noncommissioned officers for a future Polish Army.

In 1910 two legal paramilitary organizations were created in the Austrian zone of Poland — one in Lwów (now Lviv) and one in Kraków (Krakiv) — to conduct training in military science. With the permission of the Austrian authorities, Piłsudski founded a series of "sporting clubs", then the Riflemen's Association, which served as cover to train a Polish military force. In 1912 Piłsudski (using the nom de guerre, "Mieczysław") became commander-in-chief of a Riflemen's Association (Związek Strzelecki) that grew by 1914 to 12,000 men. In 1914, Piłsudski declared that "Only the sword now carries any weight in the balance for the destiny of a nation."

At a meeting in Paris in 1914, Piłsudski presciently declared that in the impending war, for Poland to regain independence, Russia must be beaten by the Central Powers (the Austro-Hungarian and German Empires), and the latter powers must in their turn be beaten by France, Britain and the United States. By contrast, Roman Dmowski, Piłsudski's rival, believed that the best way to achieve a unified and independent Poland was to support the Triple Entente against the Central Powers.

At the outbreak of World War I, on August 3, in Kraków, Piłsudski formed a small cadre military unit, the First Cadre Company, from members of the Riflemen's Association and Polish Rifle Squads. That same day, a cavalry unit under Władysław Belina-Prażmowski was sent to reconnoitre across the Russian border, even before the official declaration of war between Austria-Hungary and Russia, which ensued on August 6. Piłsudski's strategy was to send his forces north across the border into Russian Poland, into an area which the Russian Army had evacuated, in the hope of breaking through to Warsaw and sparking a national uprising. Using his limited forces, in those early days he backed his orders with the sanction of a fictitious "National Government in Warsaw", and bent and stretched Austrian orders to the utmost, taking initiatives, moving forward and establishing Polish institutions in liberated towns, while the Austrians saw his forces as good only for scouting or for supporting main Austrian formations. On August 12, 1914, Piłsudski's forces took the town of Kielce, of Kielce Governorate, but Piłsudski found the populace less supportive than he had expected.

Soon afterward he officially established the Polish Legions, taking personal command of their First Brigade, which he would lead successfully into several victorious battles. He also secretly informed the British government in the fall of 1914 that his Legions would never fight France or Britain, only Russia. Piłsudski decreed that Legions' personnel were to be addressed by the French Revolution inspired "Citizen" (Obywatel), and he himself was referred to as "the Commandant" ("Komendant"). Piłsudski enjoyed extreme respect and loyalty from his men which would remain for years to come. The Polish Legions fought against Russia at the side of the Central Powers until 1917. Soon after forming the Legions, also in 1914, Piłsudski set up another organization, the Polish Military Organisation (Polska Organizacja Wojskowa), which served as a precursor Polish intelligence agency and was designed to perform espionage and sabotage missions.

In mid-1916, after the Battle of Kostiuchnówka (July 4–6, 1916), in which the Polish Legions delayed a Russian offensive at a cost of over 2,000 casualties, Piłsudski demanded that the Central Powers issue a guarantee of independence for Poland. He backed this demand with his own proffered resignation and that of many of the Legions' officers. On November 5, 1916, the Central Powers proclaimed the "independence" of Poland, hoping to increase the number of Polish troops that could be sent to the eastern front against Russia, thereby relieving German forces to bolster the western front. Piłsudski agreed to serve in the Regency Kingdom of Poland created by the Central Powers, and acted as minister of war in the newly formed Polish Regency government; as such he was responsible for the Polnische Wehrmacht. After the Russian Revolution in early 1917, and in view of the worsening situation of the Central Powers, Piłsudski took an increasingly uncompromising stance, insisting that his men no longer be treated as "German colonial troops" and only be used to fight Russia. Anticipating the Central Powers' defeat in the war, he did not wish to be allied with the losing side. In the aftermath of a July 1917 "Oath Crisis" when Piłsudski forbade Polish soldiers to swear an oath of loyalty to the Central Powers, he was arrested and imprisoned at Magdeburg; the Polish units were disbanded, and the men were incorporated into the Austro-Hungarian Army, while the Polish Military Organization began attacking German targets. Piłsudski's arrest greatly enhanced his reputation among Poles, many of whom began to see him as the most determined Polish leader, willing to take on all the partitioning powers.

On November 8, 1918, three days before the Armistice, Piłsudski and his colleague, Colonel Kazimierz Sosnkowski, were released by the Germans from Magdeburg and soon — like Vladimir Lenin before them — placed on a private train, bound for their national capital, as the collapsing Germans hoped that Piłsudski would create a force friendly to them. On November 11, 1918, in Warsaw, Piłsudski was appointed Commander in Chief of Polish forces by the Regency Council and was entrusted with creating a national government for the newly independent country. On that very day (which would become Poland's Independence Day), he proclaimed an independent Polish state. That week, too, Piłsudski also negotiated the evacuation of the German garrison from Warsaw and of other German troops from the "Ober Ost" authority. Over 55,000 Germans would peacefully depart Poland, leaving their weapons to the Poles. In coming months, over 400,000 total would depart Polish territories. On November 14, 1918, Piłsudski was asked to provisionally supervise the running of the country. On November 22 he officially received, from the new government of Jędrzej Moraczewski, the title of Provisional Chief of State (Naczelnik Państwa) of renascent Poland.

Various Polish military organizations and provisional governments (the Regency Council in Warsaw; Ignacy Daszyński's government in Lublin; and the Polish Liquidation Committee in Kraków) bowed to Piłsudski, who set about forming a new coalition government. It was predominantly socialist and introduced many reforms long proclaimed as necessary by the Polish Socialist Party, such as the eight-hour day, free school education, and women's suffrage. This was necessary to avoid major unrest. However, Piłsudski believed that as head of state he must be above partisan politics. The day after his arrival in Warsaw, he met with old colleagues from underground days, who addressed him socialist-style as "Comrade" ("Towarzysz") and asked his support for their revolutionary policies; he refused it and answered: "Comrades, I took the red tram of socialism to the stop called Independence, and that's where I got off. You may keep on to the final stop if you wish, but from now on let's address each other as 'Mister' [rather than continue using the socialist term of address, 'Comrade']!" He declined to support any one party and did not form any political organization of his own; instead, he advocated creating a coalition government. He also set about organizing a Polish army out of Polish veterans of the German, Russian and Austrian armies.

In the days immediately after World War I, Piłsudski attempted to build a government in a shattered country. Much of former Russian Poland had been destroyed in the war, and systematic looting by the Germans had reduced the region's wealth by at least 10%. A British diplomat who visited Warsaw in January 1919 reported: "I have nowhere seen anything like the evidences of extreme poverty and wretchedness that meet one's eye at almost every turn". In addition, the country had to unify the disparate systems of law, economics, and administration in the former German, Austrian and Russian sectors of Poland. There were nine legal systems, five currencies, 66 types of rail systems (with 165 models of locomotives), which all had to be consolidated on an expedited basis. Wacław Jędrzejewicz, in Piłsudski: A Life for Poland, describes Piłsudski as very deliberate in his decision-making. He collected all available pertinent information, then took his time weighing it before arriving at a final decision. Piłsudski drove himself hard, working all day and all night. He maintained a spartan lifestyle, eating plain meals alone at an inexpensive restaurant. Though Piłsudski was popular with much of the Polish public, his reputation as a loner (the result of many years' underground work), as a man who distrusted almost everyone, led to strained relations with other Polish politicians.

Piłsudski and the first Polish government were distrusted in the West because Piłsudski had cooperated with the Central Powers in 1914–17 and because the governments of Daszyński and Jędrzej Moraczewski were primarily socialist. It was not until January 1919, when the world-famous pianist and composer Ignacy Paderewski became prime minister and foreign minister of a new government, that it was recognized in the West. That still left two separate governments claiming to be Poland's legitimate government: Piłsudski's in Warsaw, and Dmowski's in Paris. To ensure that Poland have a single government and to avert civil war, Paderewski met with Dmowski and Piłsudski and persuaded them to join forces, with Piłsudski acting as Provisional Chief of State and Commander-in-Chief while Dmowski and Paderewski represented Poland at the Paris Peace Conference. Articles 87–93 of the Versailles Treaty and the Little Treaty of Versailles, signed on June 28, 1919, formally established Poland as an independent and sovereign state in the international arena. Piłsudski often clashed with Dmowski, at variance with the latter's vision of the Poles as the dominant nationality in renascent Poland, and irked by Dmowski's attempt to send the Blue Army to Poland through Danzig, Germany (now Gdańsk, Poland). On January 5, 1919, some of Dmowski's supporters (Marian Januszajtis-Żegota and Eustachy Sapieha) attempted a coup against Piłsudski and Prime Minister Moraczewski, but failed.

On February 20, 1919, Piłsudski declared that he would return his powers to the newly elected Polish parliament (Sejm). However, the Sejm reinstated his office in the Little Constitution of 1919. The word "Provisional" was struck from his title, and Piłsudski would hold the office until December 9, 1922, when Gabriel Narutowicz was elected the first president of Poland.

Piłsudski's major foreign-policy initiative at this time was a proposed federation (to be called "Międzymorze", Polish for "Between Seas", and also known from the Latin as "Intermarum", stretching from the Baltic to the Black Sea) of Poland with the independent Baltic states and Belarus and Ukraine, somewhat in emulation of the pre-partition Polish-Lithuanian Commonwealth. Piłsudski's plan met with opposition from most of the prospective member states — who refused to relinquish any of their hard-won independence — as well as from the Allied powers, for whom it would be too bold a change to the existing balance of power structure. According to historian George Sanford, around 1920 Piłsudski came to realize the infeasibility of this version of his Intermarum project. Instead of a Central- and East-European alliance, there soon appeared a series of border conflicts, including the Polish-Ukrainian War (1918–19), the Polish-Lithuanian War (1920, culminating in Żeligowski's Mutiny), Polish-Czechoslovak border conflicts (beginning in 1918), and most notably the Polish-Soviet War (1919–21). Winston Churchill commented: "The war of giants has ended, the wars of the pygmies begin."

In the aftermath of World War I, there was unrest on all Polish borders. Regarding Poland's future frontiers, Piłsudski said, "All that we can gain in the west depends on the Entente — on the extent to which it may wish to squeeze Germany", while in the east "there are doors that open and close, and it depends on who forces them open and how far." In 1918 in the east, Polish forces clashed with Ukrainian forces in the Polish-Ukrainian War, and Piłsudski's first orders as Commander-in-Chief of the Polish Army, on November 12, 1918, were to provide support for the Polish struggle in Lviv. However, while Ukrainians were the first clear enemies, it soon became apparent that the various Ukrainian factions were not the real powers in that region. Coming months and years would show that the Bolsheviks were in fact the most dangerous enemies, not only of renascent Poland, but of the Ukrainians. Piłsudski was aware that the Bolsheviks were no friends of independent Poland, and that war with them was inevitable. He viewed their advance west as a major problem, but also considered the Bolsheviks less dangerous for Poland than their Russian Civil War opponents. These "White Russians" — representative of the old Russian Empire — were willing to accept only limited independence for Poland, probably within borders similar to those of the former Congress Poland, and clearly objected to Polish control of Ukraine, which was crucial for Piłsudski's Intermarum project. This was in contrast to the Bolsheviks, who proclaimed the partitions of Poland null and void. Piłsudski thus speculated that Poland would be better off with the Bolsheviks, alienated from the Western powers, than with a restored Russian Empire. By ignoring the strong pressures from the Entente Cordiale to join the attack on Vladimir Lenin's struggling Soviet government, Piłsudski probably saved the Bolshevik government in the summer and fall of 1919.

In the wake of the Russian westward offensive of 1918–1919 and of a series of escalating battles which resulted in the Poles advancing eastward, on April 21, 1920, Marshal Piłsudski (as his rank had been since March 1920) signed a military alliance (the Treaty of Warsaw) with Ukrainian leader Symon Petliura to conduct joint operations against Soviet Russia. The goal of the Polish-Ukrainian treaty was to establish an independent Ukraine in alliance with Poland. In return, Petliura gave up Ukrainian claims to eastern Galicia, for which he was denounced by eastern-Galician Ukrainian leaders. The Polish and Ukrainian armies, under Piłsudski's command, launched a successful offensive against the Russian forces in Ukraine. On May 7, 1920, with remarkably little fighting, they captured Kiev. The Bolshevik leadership framed the Polish actions as an invasion; in response, thousands of officers and deserters joined the army, and thousands of civilians volunteered for war work. The Soviets launched a counter-offensive from Belarus and counter-attacked in Ukraine, advancing into Poland in a drive toward Germany to encourage the German Communist Party in its struggle to take power. Soviet confidence soared. The Soviets announced their plans to invade western Europe; Soviet communist theoretician Nikolai Bukharin, writing in Pravda, hoped for the resources to carry the campaign beyond Warsaw "straight to London and Paris". Soviet General Mikhail Tukhachevsky's order of the day for July 2, 1920, read: "To the West! Over the corpse of White Poland lies the road to worldwide conflagration. March upon Vilnius, Minsk, Warsaw!" and "onward to Berlin over the corpse of Poland!"

On July 1, 1920, in view of the rapidly advancing Soviet offensive, Poland's parliament, the Sejm, formed a Council for Defense of the Nation. It was chaired by Piłsudski and was to provide expeditious decision-making and temporarily supplant the fractious Sejm. The National Democrats, however, contended that the string of Bolshevik victories had been Piłsudski's fault and demanded that he resign; some even accused him of treason. Their July 19 failure to carry a vote of no-confidence in the council led to Roman Dmowski's withdrawal from it. On August 12 Piłsudski tendered his resignation to Prime Minister Wincenty Witos, offering to be the scapegoat if the military solution failed, but Witos refused to accept his resignation. The Entente pressured Poland to surrender and enter into negotiations with the Bolsheviks. Piłsudski, however, was a staunch advocate of continuing the fight. As Norman Davies noted, at that time, especially abroad, "Piłsudski had nothing of his later prestige. As a pre-war revolutionary he led his party to splits and quarrels; as a general in the WWI he led his legions to internment and disbanding; as a marshal of the Polish Army he led it to Kiev and Vilnius, both now lost to Poles. He left the Polish Socialist Party and his Austro-German allies; refused to ally himself with Entente. In France and England he was considered a treasonous ally who leads Poland into destruction; in Russia he was seen as a false servant of the allies, who will lead imperialism to ruin. All – from Lenin to Lloyd George, from Pravda to Morning Star – considered him a military and political failure. In August 1920 all were in agreement that his catastrophic career will be crowned with the fall of Warsaw."

Yet over the next few weeks, Poland's risky, unconventional strategy at the August 1920 Battle of Warsaw halted the Soviet advance. The Polish plan was developed by Piłsudski and others, including Tadeusz Rozwadowski. Later, some supporters of Piłsudski would seek to portray him as the sole author of the Polish strategy, while opponents would seek to minimize his role. In the West for a long time a myth persisted that it was General Maxime Weygand of the French military mission to Poland who had saved Poland; modern scholars, however, are in agreement that Weygand's role was minimal at best. Piłsudski's plan called for Polish forces to withdraw across the Vistula River and defend the bridgeheads at Warsaw and on the Wieprz River, while some 25% of available divisions concentrated to the south for a strategic counter-offensive. The plan next required two armies under General Józef Haller, facing Soviet frontal attack on Warsaw from the east, to hold their entrenched positions at all costs. At the same time, an army under General Władysław Sikorski was to strike north from outside Warsaw, cutting off Soviet forces that sought to envelope the Polish capital from that direction. The most important role, however, was assigned to a relatively small, approximately 20,000-man, newly assembled "Reserve Army" (also known as the "Strike Group", "Grupa Uderzeniowa"), comprising the most determined, battle-hardened Polish units and commanded personally by Piłsudski. Their task was to spearhead a lightning northward offensive, from the Vistula-Wieprz triangle south of Warsaw, through a weak spot identified by Polish intelligence between the Soviet Western and Southwestern Fronts. That offensive would separate the Soviet Western Front from its reserves and disorganize its movements. Eventually, the gap between Sikorski's army and the "Strike Group" would close near the East Prussian border, bringing about the destruction of the encircled Soviet forces.

At the time, Piłsudski's plan was strongly criticized, and only the desperate situation of the Polish forces persuaded other commanders to go along with it. Though based on reliable intelligence, including decrypted Soviet radio communications, the plan was termed "amateurish" by high-ranking army officers and military experts who were quick to point out Piłsudski's lack of formal military education. When a copy of the plan fell into Soviet hands, Soviet commander Mikhail Tukhachevsky thought it a ruse and disregarded it. Days later, the Soviets paid dearly for this when, during the Battle of Warsaw, the overconfident Red Army suffered one of its greatest defeats ever. A National Democrat Sejm deputy, Stanisław Stroński, coined the phrase, "Miracle at the Vistula" ("Cud nad Wisłą"), to express his disapproval of Piłsudski's "Ukrainian adventure". Stroński's phrase was adopted as praise for Piłsudski by some patriotically or piously minded Poles, who were unaware of Stroński's ironic intent. A junior member of the French military mission, Charles de Gaulle, would later adopt some lessons from the Polish-Soviet War as well as from Piłsudski's career.

In February 1921, Piłsudski visited Paris, where in negotiations with French president Alexandre Millerand he laid the foundations for the Franco-Polish Military Alliance that would be signed later that year. The Treaty of Riga, which ended the Polish-Soviet War in March 1921, partitioned Belarus and Ukraine between Poland and Russia. Piłsudski called the treaty an "act of cowardice". The treaty, and Piłsudski-approved General Lucjan Żeligowski's capture of Vilnius from the Lithuanians, marked an end to this incarnation of Piłsudski's federalist Intermarum plan.

On September 25, 1921, when Piłsudski visited Lwów (now Lviv) for the opening of the first Eastern Trade Fair (Targi Wschodnie), he was the target of an unsuccessful assassination attempt by Stepan Fedak, acting on behalf of Ukrainian independence organizations, including the Ukrainian Military Organization.

After the Polish Constitution of March 1921 severely limited the powers of the presidency (intentionally, to prevent a President Piłsudski from waging war), Piłsudski declined to run for the office. On December 9, 1922, the Polish National Assembly elected Gabriel Narutowicz of PSL Wyzwolenie; his election, opposed by the right-wing parties, caused public unrest. On December 14, at the Belweder Palace, Piłsudski officially transferred his powers as Chief of State to his friend Narutowicz; the Naczelnik was replaced by the President. Two days later, on December 16, 1922, Narutowicz was shot dead by a right-wing painter and art critic, Eligiusz Niewiadomski, who had originally wanted to kill Piłsudski but had changed his target, influenced by National-Democrat anti-Narutowicz propaganda. For Piłsudski this was a major shock, an event that shook his belief that Poland could function as a democracy and made him favor government by a strong hand. He became Chief of the General Staff and, together with Minister of Military Affairs Władysław Sikorski, managed to stabilize the situation, quelling unrest with a brief state of emergency. Stanisław Wojciechowski of PSL Piast, another of Piłsudski's old colleagues, was elected the new president, and Wincenty Witos, also of PSL Piast, became prime minister. But the new government — pursuant to the Lanckorona Pact, an alliance among the centrist PSL Piast and the right-wing National Populist Union and Christian Democrat parties — contained right-wing enemies of Piłsudski, people whom he held morally responsible for Narutowicz's death and whom he found it impossible to work with. On May 30, 1923, Piłsudski resigned as Chief of the General Staff.

After General Stanisław Szeptycki proposed that the military should be more closely supervised by civilian authorities, Piłsudski criticized this as an attempt to politicize the army, and on June 28 he resigned his last political appointment. The same day, the Sejm's left-wing deputies voted a resolution thanking him for his past work. Piłsudski went into retirement in Sulejówek, outside Warsaw, at his country manor, "Milusin", which had been presented to him by his former soldiers. There he settled down to supporting his family by writing a series of political and military memoirs, including Rok 1920 (The Year 1920). Meanwhile Poland's economy was in shambles. Hyperinflation fueled public unrest, and the government was unable to find a quick solution to the mounting unemployment and economic crisis. Piłsudski's allies and supporters repeatedly asked him to return to politics, and he began to create a new power base, centered around former members of the Polish Legions and the Polish Military Organization as well as some left-wing and intelligentsia parties. In 1925, after several governments had resigned in short order and the political scene was becoming increasingly chaotic, Piłsudski became more and more critical of the government, eventually issuing statements demanding the resignation of the Witos cabinet.

When the Chjeno-Piast coalition, which Piłsudski had strongly criticized, formed a new government, on May 12–14, 1926, Piłsudski returned to power in a coup d'état (the May Coup), supported by the Polish Socialist Party, Liberation, the Peasant Party, and even the Polish Communist Party. Piłsudski had hoped for a bloodless coup, but the government had refused to back down; 215 soldiers and 164 civilians had been killed, and over 900 persons had been wounded. On May 31, the Sejm elected Piłsudski president of the Republic. Piłsudski, however, aware of the presidency's limited powers, refused the office. Another of his old friends, Ignacy Mościcki, was elected in his stead. Piłsudski's formal offices — apart from two terms as prime minister in 1926–28 and 1930 — would for the most part remain limited to those of minister of defense and General Inspector of the Armed Forces. He also served as minister of military affairs and chairman of the war council. Piłsudski had no plans for major reforms; he quickly distanced himself from the most radical of his left-wing supporters, declaring that his coup was to be a "revolution without revolutionary consequences". His goals were to stabilize the country, reduce the influence of political parties, which he blamed for corruption and inefficiency, and strengthen the army.

In internal politics, Piłsudski's coup entailed sweeping limitations on parliamentary government, as his Sanation regime (1926 – 1939) — at times employing authoritarian methods — sought to "restore public life to moral health". From 1928, the Sanation authorities were represented in the sphere of practical politics by the Non-partisan Bloc for Cooperation with the Government (BBWR). Popular support and an effective propaganda apparatus allowed Piłsudski to maintain his authoritarian powers, which could not be overruled by the president, who was appointed by Piłsudski, not by the Sejm. The powers of the Sejm were curtailed by constitutional amendments introduced soon after the coup, on August 2, 1926. From 1926 to 1930, Piłsudski relied chiefly on propaganda to weaken the influence of opposition leaders. The culmination of his dictatorial and supralegal policies came in 1930 with the imprisonment and trial of certain political opponents (the Brest trials) on the eve of the 1930 legislative elections, and with the 1934 establishment of a prison for political prisoners at Bereza Kartuska (today Biaroza), where some prisoners were brutally mistreated. After theBBWR's 1930 victory, Piłsudski left most internal matters in the hands of his "colonels", while he himself concentrated on military and foreign affairs. He came under considerable criticism for his treatment of political opponents, and their 1930 arrest and imprisonment was internationally condemned and damaged Poland's reputation. Piłsudski became increasingly disillusioned with democracy in Poland. His intemperate public utterances — he called the Sejm a "prostitute" – and his sending ninety armed officers into the Sejm building in response to an impending vote of no-confidence, caused concern in contemporary and modern-day observers who have seen his actions as setting precedents for authoritarian responses to political challenges. One of Piłsudski's main goals was to transform the parliamentary system into a presidential system; however, he opposed the introduction of totalitarianism. The adoption of a new Polish constitution in April 1935, tailored by Piłsudski's supporters to his specifications — providing for a strong presidency — came too late for Piłsudski to seek that office; but the April Constitution would serve Poland up to the outbreak of World War II and would carry its Government in Exile through to the end of the war and beyond. Nonetheless, Piłsudski's government depended more on his charismatic authority than on rational legal authority. None of his followers could claim to be his legitimate heir, and after his death the Sanation structure would quickly fracture, returning Poland to the pre-Piłsudski era of parliamentary political contention.

Piłsudski's regime began a period of national stabilization and of improvement in the situation of ethnic minorities, which formed about a third of the Second Republic's population. Piłsudski replaced the National Democrats' "ethnic-assimilation" with a "state-assimilation" policy: citizens were judged not by their ethnicity but by their loyalty to the state. Widely recognized for his opposition to the National Democrats antisemitic policies, he extended his policy of "state-assimilation" to Polish Jews. The years 1926–35, and Piłsudski himself, were favorably viewed by many Polish Jews whose situation improved especially under Piłsudski appointed Prime Minister Kazimierz Bartel. Many Jews saw Piłsudski as their only hope for restraining antisemitic currents in Poland and for maintaining public order; he was seen as a guarantor of stability and a friend of the Jewish people, who voted for him and actively participated in his political bloc. Piłsudski's death in 1935 brought a deterioration in the quality of life of Poland's Jews. During the 1930s, a combination of developments, from the Great Depression to the vicious spiral of OUN terrorist attacks and government pacifications, caused government relations with the national minorities to deteriorate. Unrest among national minorities was also related to foreign policy. Troubles followed repressions in largely Ukrainian populated eastern Galicia, where nearly 1,800 persons were arrested. Tension also arose between the government and Poland's German minority, particularly in Upper Silesia. The government did not yield to calls for antisemitic measures; but the Jews (8.6% of Poland's population) grew discontented for economic reasons that were connected with the depression. Overall, by the end of Piłsudski's life, his government's relations with national minorities were increasingly problematic.

In the military sphere, Piłsudski, who had shown himself an accomplished military strategist in engineering the "Miracle at the Vistula", has been criticized by some for subsequently concentrating on personnel management and allegedly neglecting modernization of military strategy and equipment. His experiences in the Polish-Soviet War (1919–21) may have led him to overestimate the importance of cavalry and to neglect the development of armored and air forces. Others, however, contend that, particularly from the late 1920s, he did support the development of these military branches. The limitations on Poland's military modernization in this period may have been less doctrinal than financial.

Under Piłsudski, Poland maintained good relations with neighboring Romania, Hungary and Latvia. Relations were strained with Czechoslovakia, however, and were still worse with Lithuania. Relations with Weimar Germany and the Soviet Union varied over time, but during Piłsudski's tenure could for the most part be described as neutral. Piłsudski's Promethean program, designed to weaken the Russian Empire and its successor state, the Soviet Union, by supporting nationalist independence movements of major non-Russian peoples dwelling in Russia and the Soviet Union, was coordinated from 1927 to the 1939 outbreak of World War II in Europe by the military intelligence officer, Edmund Charaszkiewicz. In the Interbellum, the Prometheist movement yielded few tangible results. Piłsudski sought to maintain his country's independence in the international arena. Assisted by his protégé, Foreign Minister Józef Beck, he sought support for Poland in alliances with western powers such as France and the United Kingdom, and with friendly, if less powerful, neighbors such as Romania and Hungary. A supporter of the Franco-Polish Military Alliance and the Polish-Romanian Alliance (part of the Little Entente), Piłsudski was disappointed by the French and British policy of appeasement evident in those countries' signing of the Locarno Treaties. Piłsudski therefore aimed also to maintain good relations with the Soviet Union and Germany; hence Poland signed non-aggression pacts with both its powerful neighbors: the 1932 Soviet-Polish Non-Aggression Pact, and the 1934 German-Polish Non-Aggression Pact. The two treaties were meant to strengthen Poland's position in the eyes of its allies and neighbors. Piłsudski himself was acutely aware of the shakiness of the pacts, and commented: "Having these pacts, we are straddling two stools. This cannot last long. We have to know from which stool we will tumble first, and when that will be." Critics of the two non-aggression pacts have accused Piłsudski of underestimating Hitler's aggressiveness and of giving Germany time to rearm; and of allowing Stalin to eliminate opposition — primarily in Ukraine — that had been supported by Piłsudski's Promethean program.

After Adolf Hitler came to power in January 1933, Piłsudski is rumored to have proposed to France a preventive war against Germany. It has been argued that Piłsudski may have been sounding out France regarding possible joint military action against Germany, which had been openly rearming in violation of the Versailles Treaty. French disinterest may have been a reason why Poland signed the German-Polish Non-Aggression Pact of January 1934. Little evidence has, however, been found in French or Polish diplomatic archives that such a proposal for preventive war was ever actually advanced. Hitler repeatedly suggested a German-Polish alliance against the Soviet Union, but Piłsudski declined, instead seeking precious time to prepare for potential war with Germany or with the Soviet Union. Hitler, who admired Piłsudski's leadership and his successful coup, also kept hoping to meet personally with Piłsudski, but again was rebuffed. Just before his death, Piłsudski told Józef Beck that it must be Poland's policy to maintain neutral relations with Germany and keep up the Polish alliance with France, and to improve relations with the United Kingdom.

By 1935, unbeknown to the public, Piłsudski had for several years been in declining health. On May 12, 1935, he died of liver cancer at Warsaw's Belweder Palace. The celebration of his life had begun spontaneously within half an hour after his death had been announced. It was led by military personnel — former Legionnaires, members of the Polish Military Organization, veterans of the wars of 1919–21, and his political collaborators from his time as Chief of State and, later, prime minister and the general inspector.

The Polish Communist Party immediately attacked Piłsudski as a fascist and capitalist. Other opponents of the Sanation regime, however, were more civil; socialists (such as Ignacy Daszyński and Tomasz Arciszewski) and Christian Democrats (represented by Ignacy Paderewski, Stanisław Wojciechowski and Władysław Grabski) expressed condolences. The peasant parties split in their reactions (Wincenty Witos voicing criticism of Piłsudski, but Maciej Rataj and Stanisław Thugutt being supportive), while Roman Dmowski's National Democrats expressed a toned-down criticism.

Condolences were expressed by Polish Catholic clergy — by Poland's Primate August Hlond — as well as by Pope Pius XI, who called himself a "personal friend" of the Marshal. Notable appreciation for Piłsudski was expressed by Poland's ethnic and religious minorities. Eastern Orthodox, Greek Orthodox, Protestant, Judaic and Islamic organizations expressed condolences, praising Piłsudski for his policies of religious tolerance. His death was a shock to members of the Jewish minority, who even years after remembered him as a very good man who protected Jews. Mainstream organizations of ethnic minorities similarly expressed their support for his policies of ethnic tolerance, though he was criticized by, in addition to the Polish communists, by the Jewish Labour Bund, and by Ukrainian, German and Lithuanian extremists.

On the international scene, Pope Pius XI held a special ceremony May 18 in the Holy See, a commemoration was conducted at League of Nations Geneva headquarters, and dozens of messages of condolence arrived in Poland from heads of state across the world, including Germany's Adolf Hitler, the Soviet Union's Joseph Stalin, Italy's Benito Mussolini and King Victor Emmanuel III, France's Albert Lebrun and Pierre-Étienne Flandin, Austria's Wilhelm Miklas, Japan's Emperor Hirohito, and Britain's King George V.

Ceremonies, masses and an enormous funeral were held; a funeral train toured Poland. The Polish mint issued a silver 10-złoty commemorative coin featuring the Marshal's profile. A series of postcards, stamps and postmarks was also released. After a two-year display at St. Leonard's Crypt in Kraków's Wawel Cathedral, Piłsudski's body was laid to rest in the Cathedral's Crypt under the Silver Bells, except for his brain, which he had willed for study to Stefan Batory University, and his heart, which was interred in his mother's grave at Vilnius' Rasos Cemetery, where it remains. The 1937 relocation of his remains, made by his long-standing adversary Adam Sapieha, then Archbishop of Krakow, incited widespread protests that included calls for Sapieha's removal.