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The timeline is not intended to chronicle the rich history of Poland in the twentieth century, but is rather meant to outline major events in Polish history that are reflected in the collections of the Manuscript Division.
November 11: Polish Independence Day. Marshall Józef Piłsudski becomes “chief of the state”.
June 28: Signing of the Treaty of Versailles. Poland is ratified as a sovereign state and gains access to the Baltic Sea.
April 21: Signing of the Treaty of Warsaw, also known as the Polish-Ukrainian Alliance, signed during the Polish-Soviet War.
March 17: Adoption of the modern Polish constitution: the March Constitution.
November 5–12: Legislative election. Gabriel Narutowicz becomes President on December 9.
December 16: Gabriel Narutowicz is assassinated and Stanisław Wojciechowski becomes President on December 22.
May 12–14: May Coup organized and carried out by Marshal Józef Piłsudski, overthrowing the government of President Stanisław Wojciechowski and Prime Minister Wincenty Witos. A new government is installed, and Ignacy Mościcki becomes President on June 4.
March 4-11: Legislative election, often considered the last free election in Poland until 1989. Piłsudski's Nonpartisan Bloc for Cooperation with the Government, a coalition of the Sanation faction, wins the election.
July 25: Signing of the Soviet–Polish Non-Aggression Pact.
January 26: Signing of the German–Polish Non-Aggression Pact.
September 1: German Invasion of Poland.
September 17: Soviet Union invasion of Poland.
September 18: The Fall of Warsaw. Poland is occupied by October 6.
November 6: Sonderaktion Krakau terror operation taken by Nazis against university professors, targeting Poland's intellectual elite.
April–May: Katyn Massacre. One of the earliest mass shootings of prisoners of war during World War II.
May 16: Authorization of German AB-Aktion in Poland targeting Polish individuals suspected of potential anti-Nazi activity.
August 17: Signing of the Sikorski-Mayski agreement between Soviet Union and Poland signed in London.
Operation Reinhard begins - initially centered in Belzec, Sobibor, and Treblinka camps - marking the beginning of Nazi plans of extermination in Poland.
April 19 - May 16: Warsaw Ghetto Uprising, the first popular uprising in Nazi-occupied Europe.
July 11–12: Zagaje massacre. July 11, known as "Bloody Sunday," is the peak of massacres of Polish people in Volhynia and Eastern Galicia.
July 22: Proclamation of the PKWN Manifesto by Soviet-backed Polish Committee of National Liberation, operating in opposition of exiled-Polish government in London.
August 1–October 2: Warsaw Uprising. The non-Communist underground resistance army, the Polish Home Army (Armia Krajowa; AK), rose against German occupation in an effort to liberate Warsaw. The uprising began when Soviet forces arrived along the east bank of the Vistula River. The Soviets forces did not intervene or aid the resistance fighters, and the revolt was crushed by Nazi forces.
February 11: Yalta Conference concludes.
March 17–18: Poland's Weddings to the Sea in Mrzeżyno and Kołobrzeg, symbolizing Poland's restored access to the Baltic Sea.
May 8: End of World War II in Europe.
August 2: Potsdam Conference concludes between the Soviet Union, the United Kingdom, and the United States.
June 30: People's referendum, also known as Three Times Yes (Trzy razy tak), on the authority of the State National Council.
February 19: Adoption of "Small Constitution" of 1947, a temporary constitution issued by the Sejm, and was renewed until the adoption of the new 1952 constitution.
July 6: Signing of the Treaty of Zgorzelec, also known as The Agreement Concerning the Demarcation of the Established and the Existing Polish-German State Frontier.
July 22: Adoption of the Constitution of the People's Republic of Poland. First Legislative election by the one-party rule held on October 26.
May 14: Signing of the Warsaw Pact, an alliance established between the Soviet Union and several Eastern European countries.
March 12: Death of former President and Prime Minister Bolesław Bierut. Office of Prime Minister temporarily abolished, and succeeded by Aleksander Zawadzki, Chairman of the Council of State. Once office was restored, filled by Wojciech Jaruzelski.
June 28: Poznań protests - the first of several protests held in opposition of the communist government of the Polish People's Republic.
March Political crisis: a series of protests in opposition of the communist government of the Polish People's Republic. Unrest in Poland coincided with the events of the Prague Spring in neighboring Czechoslovakia.
December 7: Signing of Treaty of Warsaw, a treaty between West Germany and the People's Republic of Poland.
December 14–19: Protests of 1970 begin. Widespread strikes take place in response to increase in cost of food and goods.
October 16: Election of Pope John Paul II.
Gdańsk Agreement, formed by striking workers as a social contract with the government and led to the formation of the independent trade union Solidarity.
August 17–21: List of demands issues by the Interfactory Strike Committee, including the right to create independent trade unions.
December 13: Martial law begins following a wave of strikes and a rise in political opposition.
July 22: Martial law ends.
Father Jerzy Popiełuszko murdered by Polish secret police.
April 4: Signing of the Round Table Agreement, legalizing trade unions, introducing a Presidential office, and forming a senate.
June 4: Parliamentary election, the first free elections in Poland since 1928.
August 24: Tadeusz Mazowiecki becomes first non-communist prime minister in the Eastern Bloc.
December 31: The People's Republic of Poland becomes the Republic of Poland.
November 14: Signing of German–Polish Border Treaty, which had been unsettled since 1945.
November 25: Presidential election; Lech Wałęsa becomes President on December 22.
July 1: Dissolution of the Warsaw Pact.
April 2: Adoption of the Constitution of the Republic of Poland.
January 1: Sixteen new voivodeships created in Polish local government reforms.
March 12: Accession of Poland to NATO.
April 16: Signing of the Treaty of Accession.
June: European Union membership referendum.
May 1: Accession of Poland to the European Union.
June 13: European Parliament election.
April 10: Polish Air Force Tu-154 crash killing Polish President Lech Kaczyński and many government and military officials.
July 4: Bronisław Komorowski elected President following the plane April crash.