The Polish-Lithuanian Commonwealth – one of the largest and most populous countries of 16th- and 17th-century Europe, with some 390,000 square miles (1,000,000 km2) and a multi-ethnic population of 11 million at its peak in the early 17th century.
The Kingdom of Poland and the Grand Duchy of Lithuania 1620, with modern borders superimposed
Born 1369, when Lithuania’s Grand Duke Jogaila married Queen regnant* Jadwiga of Poland. Ended with the Third Partition in 1795, Poland and Lithuania would not appear on maps again until 1918.
* Queen regnant = queen is reigning monarch rather than being “just” the king’s wife. QEII is a queen regnant.