Union of Lublin

The Union of Lublin (Polish: unia lubelska; Lithuanian: Liublino unija) replaced the personal union of the Crown of the Kingdom of Poland and the Grand Duchy of Lithuania with a real union and an elective monarchy, since Sigismund II Augustus, the last of the Jagiellons, remained childless after three marriages. In addition, the autonomy of Royal Prussia was largely abandoned. The Duchy of Livonia, tied to Lithuania in real union since the Union of Grodno (1566), became a Polish–Lithuanian condominium.

It was signed July 1, 1569, in Lublin, Poland, and created a single State, the Polish–Lithuanian Commonwealth. The Commonwealth was ruled by a single elected monarch who carried out the duties of King of Poland and Grand Duke of Lithuania, and governed with a common Senate and parliament (the Sejm). The Union was an evolutionary stage in the Polish–Lithuanian alliance and personal union, necessitated also by Lithuania's dangerous position in wars with Russia.

Constituting a crucial event in the history of several nations, the Union of Lublin has been viewed quite differently by many historians. Some identify it as the moment at which the Szlachta rose to the height of their power, establishing an oligarchy as opposed to absolute monarchy: a possible cause of political instability that led to the Partitions of Poland over 200 years later. Polish historians concentrate on its positive aspects, emphasizing its peaceful, voluntary creation and its role in the spreading of Polish culture. Lithuanian historians are more critical of the Union, pointing out that it was dominated by Poland.