 The partnership brought vast territories controlled by the Grand Duchy of Lithuania into Poland's sphere of influence and proved beneficial for both the Polish and Lithuanian people, who coexisted and cooperated in one of the largest political entities in Europe for the next four centuries.In the Baltic Sea region, Poland maintained an ongoing conflict with the Teutonic Knights.The struggles led to a major battle, the Battle of Grunwald of 1410, but there was also the milestone Peace of Thorn of 1466 under King Casimir IV Jagiellon; the treaty created the future Duchy of Prussia.