The Prussian Confederation was formed on this day in 1440. The predecessor to the Kingdom of Prussia, it was formed as an alliance between nineteen cities in Prussia, to oppose their overlords, the Teutonic Order, a monastic military state in modern Livonia and Lithuania. The Confederation sought to join Poland as a fief, or region, but this prompted a war between the Teutonic and Polish armies. The Prussian cities fought with the Polish, but after the war, known as the Thirteen Years’ War, ended in 1466, the resulting truce was a compromise. Western Prussia would go to Poland, while Eastern Prussia would remain with the Teutonic Order. Due to the divide between the cities, the Prussian Confederation broke up, although a long war between Poland and the Teutonic Order would break out again due to one of the Prussian cities.