 At the instigation of Duke Konrad I of Masovia, the Teutonic Knights took possession of Prussia in the 13th century and created a monastic state to administer the conquered Old Prussians.Local Old-Prussian (north) and Polish (south) toponyms were gradually Germanised.The Knights' expansionist policies, including occupation of Polish Pomerania with Gdańsk/Danzig and western Lithuania, brought them into conflict with the Kingdom of Poland and embroiled them in several wars, culminating in the Polish-Lithuanian-Teutonic War, whereby the united armies of Poland and Lithuania, defeated the Teutonic Order at the Battle of Grunwald (Tannenberg) in 1410.