The Polish-Lithuanian Commonwealth was a dual state formed in 1569, uniting the Kingdom of Poland and the Grand Duchy of Lithuania. This political entity was characterized by a unique system of governance, where both nations shared a monarch and a parliament, known as the Sejm. The Commonwealth became one of the largest and most populous countries in Europe during its height. The Commonwealth was known for its cultural diversity and religious tolerance, allowing various ethnic groups and faiths to coexist. It played a significant role in European politics until its decline in the late 18th century, leading to its eventual partitions by neighboring powers, including Russia, Prussia, and Austria.