In 1212 Ottokar I was granted a hereditary title of the King of Bohemia by the Holy Roman Emperor Frederick II. Thus began the Kingdom of Bohemia, which lasted de iure until the end of World War I. His reign marked the start of the German eastward colonization, which over time significantly altered the language composition of the Czech Lands. His son Wenceslaus I had to deal with the Mongol invasion of Europe at the start of 1240s. He managed to defend Bohemia, but Moravian lands were heavily plundered. When the Duke of Austria Frederick II died in 1246 without male heirs, Wenceslaus I tried to secure the Austrian lands by marrying his eldest son Vladislaus to Frederick's nice Gertrude. This plan failed because of Vladislaus's premature death in the year after. Wenceslaus I then decided for the invasion of Austria and he was successful. His successor, Ottokar II, continued the expansion of the realm. He gained more territory south of Austria and led two crusades against the pagan Old Prussians. He was hoping to gain the Imperial crown, but lost in the 1273 election to Rudolf of Habsburg, the first in a line of Habsburg emperors. Rudolf of Habsburg demanded that Ottokar II returns all of the lands he had acquired south of Bohemia. Ottokar refused and waged two wars against the emperor which ended with his death at the battlefield of Marchfeld in 1278.