Polish-Lithuanian Commonwealth

Coat of arms of Poland–Lithuania

The Polish-Lithuanian Commonwealth, also known as the First Polish Republic or Republic (Commonwealth) of the Two (Both) Nations (Peoples), (Polish: Pierwsza Rzeczpospolita or Rzeczpospolita Obojga Narodów; Lithuanian: Abiejų tautų respublika) or as the "First Republic," was one of the largest and most populous countries in 17th-century Europe. Its political structure — that of a semi-federal, semi-confederal aristocratic republic — was formed in 1569 by the Union of Lublin, which united the Kingdom of Poland and the Grand Duchy of Lithuania, and lasted in this form until the adoption of the Constitution of May 3, 1791. The Commonwealth covered not only the territories of what is now Poland and Lithuania, but also the entire territory of Belarus and Latvia, large parts of Ukraine and Estonia, and part of present-day western Russia (Smolensk and Kaliningrad oblasts). Originally the official languages of the Commonwealth were Polish and Latin (in the Kingdom of Poland) and Ruthenian and Lithuanian (in the Grand Duchy of Lithuania).

The Commonwealth was an extension of the Polish-Lithuanian Union, a personal union between those two states that had existed from 1386 (see Union of Krewo). The Commonwealth's political system, often called the Noble's democracy or Golden Freedom, was characterized by the sovereign's power being reduced by laws and the legislature (Sejm) controlled by the nobility (szlachta). This system was a precursor of the modern concepts of broader democracy and constitutional monarchy as well as federation. The two comprising states of the Commonwealth were formally equal, although in reality Poland was a dominant partner in the union. The Commonwealth was also notable for the world's second-oldest codified national constitution in modern history; and, despite the massive influence of the Roman Catholic Church in the Commonwealth affairs, for the state's relative religious tolerance, although the degree of it varied with time Its economy was mainly based on agriculture. While the Commonwealth's first century was a golden age for both Poland and Lithuania, the second century was marked by military defeats, a return to serfdom for the peasants (the second serfdom phenomena), and growing anarchy in political life.

The Duchy of Warsaw, established in 1807, traced its origins to the Commonwealth. Other revival movements appeared during the January Uprising (1863–64) and in the 1920s, with Józef Piłsudski's failed attempt to create a Polish-led "Międzymorze" ("Between-Seas") federation that would have included Lithuania and Ukraine. Today's Republic of Poland considers itself a successor to the Commonwealth, whereas the pre-World War II Republic of Lithuania distanced itself from any association which it considered not to have been historically beneficial to Lithuania.