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. The Ostrów Agreement did not stop attacks from the Teutonic Knights and the territorial dispute over Samogitia continued up to 1422. According to the treaty, Vytautas became the ruler of Lithuania (styled Grand Duke), but he also acknowl