The Polish-Lithuanian Union was a political alliance formed in 1569 between the Kingdom of Poland and the Grand Duchy of Lithuania. This union aimed to strengthen both states against external threats, particularly from the Teutonic Knights and the Muscovite state. It established a single state known as the Commonwealth of Poland-Lithuania, which became one of the largest and most influential countries in Europe. The union was formalized through the Union of Lublin, which created a shared parliament and a common foreign policy. This arrangement allowed for greater cooperation in military and economic matters, fostering a unique cultural and political identity that blended Polish and Lithuanian traditions. The Commonwealth lasted until the late 18th century, when it was eventually partitioned by neighboring powers.