The German–Polish War was a conflict fought between 1028 and 1031. It was fought by Holy Roman Empire led by Conrad II, Duchy of Bohemia led by Bretislav I, Kievan Rus' led by Yaroslav the Wise and, from 1031, Kingdom of Hungary led by Stephen I, against Kingdom of Poland led by Mieszko II Lambert and, until 1031, Kingdom of Hungary led by Stephen I. The war had begun with Polish attacks on Saxony within the Holy Roman Empire. Following that, the Empire, and Kivean Rus' had attacked Poland winning the war in 1031. Following the German victory, Mieszko II Lambert was forced to abdicate, losing the title of the King of Poland, and his country being reformed into Duchy of Poland with Bezprym as a duke.