Polish–Teutonic War (1519–1521)
In the late 1490s, the Order developed the idea of electing only an Imperial Prince as future Grand Master, who as subject to the Emperor could resist having to pay homage to Kings of Poland.
Frederick died in December 1510, and Albert of Hohenzollern was chosen as his successor early in 1511 in the hope that his relationship to his maternal uncle, Sigismund I the Old, Grand Duke of Lithuania and King of Poland, would facilitate a settlement of the disputes over eastern Prussia.
As war over the Order's existence appeared inevitable, Albert made strenuous efforts to secure allies and carried on protracted negotiations with Emperor Maximilian I.
In July, the Teutonic army started an offensive, attacking Masovia, Warmia, and Łomża territories, laying siege to Lidzbark Warmiński.
The Teutonic Knights seized their chance and launched a counteroffensive, taking Nowe Miasto Lubawskie and approaching Płock and Olsztyn.
[1][2] At that point, the Ottoman Empire invaded Hungary, and the new Holy Roman Emperor, Charles V, demanded that the Teutonic Knights and Poles stop their hostilities and aid the defense of Europe against the infidels.
Eventually, in the town Wittenberg, Saxony, Albert met and was advised by Dr. Martin Luther (1483-1546), to abandon the rules of his Order, to marry, and to convert Prussia into a hereditary duchy for himself.
He resigned from the Hochmeister office to assume from his uncle, the King of Poland and Grand Duke of Lithuania, Sigismund I the Old (1467-1548, reigned 1506-1548), the Prussian Homage, the hereditary rights to the now-secularized Duchy of Prussia, as a vassal, pledging loyalty to the Polish Crown.
The Prussian Landtag diet assembled in the Baltic Sea port town of Königsberg (modern 21st century city of Kaliningrad since 1945, World War II in small remnant of old German territory of East Prussia, now small separated territory sandwiched between modern Poland and Lithuania, attached to Russia / Russian Federation), where all "Stände", led by the influential Bishop of Samland George of Polentz, embraced both the new Duke and Protestant Reformation to Lutheran faith.
