Polish–Lithuanian Commonwealth
The Polish–Lithuanian Commonwealth, also referred to as Poland–Lithuania or the First Polish Republic (Polish: I Rzeczpospolita), was a federative real union between the Kingdom of Poland and the Grand Duchy of Lithuania, existing from 1569 to 1795. This state was among the largest, most populated countries of 16th- to 18th-century Europe.
Source: Wikipedia — Polish–Lithuanian Commonwealth (CC BY-SA 4.0)