The Polish–Lithuanian Commonwealth – formally, the Crown of the Kingdom of Poland and the Grand Duchy of Lithuania and, after 1791, the Commonwealth of Poland – was a dual state, a bi-confederation of Poland and Lithuania ruled by a common monarch, who was both King of Poland and Grand Duke of Lithuania. It was one of the largest[4][5] and most populous countries of 16th– to 17th-century Europe. At its largest territorial extent, in the early 17th century, the Commonwealth covered almost 400,000 square miles (1,000,000km2)[6] and sustained a multi-ethnic population of 11 million.[7]

The Commonwealth was established by the Union of Lublin in July 1569, but the Crown of the Kingdom of Poland and the Grand Duchy of Lithuania had been in a de facto personal union since 1386 with the marriage of the Polish queen Hedwig and Lithuania's Grand Duke Jogaila, who was crowned King jure uxoris Władysław II Jagiełło of Poland. The First Partition of Poland in 1772 and the Second Partition of Poland in 1793 greatly reduced the state's size and the Commonwealth collapsed as an independent state following the Third Partition of Poland in 1795.