The Polish–Lithuanian Commonwealth was formed by the 1569 Union of Lublin between the Kingdom of Poland and the Grand Duchy of Lithuania, and lasted until 1795. The new Commonwealth was the largest and one of the most populous countries of 16th- and 17th-century Europe.[2][3][4][5]
The new union possessed features unique among contemporary states: the Commonwealth's political system (known alternately as the Noble's Democracy or Golden Freedom) was characterized by strict checks upon monarchical power. These checks were enacted by a legislature (Sejm) controlled by the nobility (szlachta). This idiosyncratic system was a precursor to modern concepts of democracy,[6] constitutional monarchy[7][8][9] and federation.[10] The two component states of the Commonwealth were formally equal, yet Poland was the dominant partner in the union.[11]
The Polish–Lithuanian Commonwealth was marked by high levels of ethnic diversity and by unusual religious tolerance,[12][13] though the degree of religious tolerance varied over time.[14]
After several decades of power and greatness,[15][16][17] the Commonwealth entered a period of protracted political,[9][18] military and economic[19] decline. Its growing weakness led to its partitioning among its more powerful neighbors, Austria, Prussia and Russia, during the late 18th century. Shortly before its demise, the Commonwealth adopted a massive reform effort and enacted the Constitution of May 3, 1791, which has been described as the second oldest codified national constitution of modern history.[20][21][22][23]
The official name of the Commonwealth was Kingdom of Poland and Grand Duchy of Lithuania (Polish: Królestwo Polskie i Wielkie Księstwo Litewskie, Lithuanian: Lenkijos Karalystė ir Lietuvos Didžioji Kunigaikštystė, Belarusian: Каралеўства Польскае і Вялікае Княства Літоўскае). It was referred to in written sources prior to the 18th century by its Latin name Regnum Poloniae Magnusque Ducatus Lithuaniae. Since the 17th century it was usually referred to as The Most Serene Commonwealth/Republic of Poland[24] (Polish: Najjaśniejsza Rzeczpospolita Polska, Latin: Serenissima Res Publica Poloniae) in international diplomatic correspondence. Its inhabitants referred to it in Polish as "Rzeczpospolita" (Ruthenian: Рѣч Посполита, Lithuanian: Žečpospolita). Foreigners often simply called it Poland, applying the pars pro toto synecdoche.
The recently widespread Polish term "Rzeczpospolita Obojga Narodów" ("The Commonwealth of Both/Two Nations") was coined only in the 20th century.[25]