Polish–Teutonic War of 1519–1521 (, horsemen's war, , Prussian War) was the war between the Kingdom of Poland and the Teutonic Knights, fought from 1519 to 1521. The war ended with the armistice in 1521. Four years later, with the Treaty of Kraków, part of the Catholic Monastic state of the Teutonic Knights became secularized as the Duchy of Prussia. The reigning Grand Master Albert of Hohenzollern-Brandenburg-Ansbach became the first Duke of Prussia by paying the Prussian Homage as vassal to his uncle, Polish king Sigismund I the Old.