Ostrów Agreement

The Ostrów or Astrava Agreement (Lithuanian: Astravos sutartis, Belarusian: Востраўскае пагадненне, Polish: Ugoda w Ostrowie) was a treaty between Jogaila (Władysław II Jagiełło), King of Poland and Grand Duke of Lithuania, and his cousin Vytautas the Great, signed on 4 August 1392. The treaty ended the destructive Lithuanian Civil War, launched in 1389 by Vytautas who hoped to gain political power, and concluded the power struggle between the two cousins that erupted in 1380 after Jogaila secretly signed the Treaty of Dovydiškės with the Teutonic Knights. According to the treaty Vytautas became ruler of Lithuania on behalf of his cousin (though he de facto wielded power of the Grand Duke). The Ostrów Agreement did not stop attacks from the Teutonic Knights and the territorial dispute over Samogitia continued up to 1422. The details of the Polish–Lithuanian relationship were clarified in several later treaties, including the Union of Vilnius and Radom in 1401 (which made Vytautas a formal Grand Duke alongside Jogaila) and Union of Horodło in 1413.