The Polish-Lithuanian Commonwealth, also known as the "Republic of the Two Nations" 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 oblast). By the 18th century, the Commonwealth was facing many internal problems and was vulnerable to foreign influences. The destabilization of the political system brought it to the brink of anarchy. Attempts at reform, such as those made by the Four-Year Sejm of 1788– 1792, which culminated in the May 3rd Constitution of 1791, came too late, and the country was partitioned in three stages by the neighboring Russian Empire, Kingdom of Prussia, and the Habsburg Monarchy. By 1795 the Polish–Lithuanian Commonwealth had been completely erased from the map of Europe.
