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Historical background

In 1230, the Teutonic Knights, a crusading military order, moved to the Kulmerland (today within the Kuyavian-Pomeranian Voivodeship) and, upon the request of Konrad I, king of the Masovian Slavs, launched the Prussian Crusade against the pagan Prussian clans. With support from the Pope and Holy Roman Emperor, the Teutons conquered and converted the Prussians by the 1280s and shifted their attention to the pagan Grand Duchy of Lithuania. For about a hundred years the Knights fought the Lithuanian Crusade raiding the Lithuanian lands, particularly Samogitia as it separated the Knights in Prussia from their branch in Livonia. The Lithuanians first gave up Samogitia during the Lithuanian Civil War (1381–84) in the Treaty of Dubysa. The territory was used as a bargaining chip to ensure Teutonic support for one of the sides in the internal power struggle.

In 1385, Grand Duke Jogaila of Lithuania proposed to marry reigning Queen Jadwiga of Poland in the Union of Kreva. Jogaila converted to Christianity and was crowned as the King of Poland thus creating a personal union between the Kingdom of Poland and Grand Duchy of Lithuania. The official Lithuanian conversion to Christianity removed the religious rationale for the Order's activities in the area. However the Knights responded by publicly contesting the sincerity of Jogaila's conversion, bringing the charge to a papal court. The territorial disputes continued over Samogitia, which was in Teutonic hands since the Peace of Raciąż of 1404. Poland also had territorial claims against the Knights in Dobrzyń Land and Danzig (Gdańsk), but the two states were largely at peace since the Treaty of Kalisz (1343). The conflict was also motivated by trade considerations: the Knights controlled lower reaches of the three largest rivers (Neman, Vistula and Daugava) in Poland and Lithuania.