But most dangerous were his disputes with Emperor Frederick II of Hohenstaufen in the course of the rebellion of the emperor's son Henry VII. Emperor Frederick ostracized the duke in 1236 and gave permission to King Wenceslaus I of Bohemia to invade the Austrian lands.
But most dangerous were his disputes with the Hohenstaufen Emperor Frederick II in the course of the rebellion of the emperor's son Henry (VII), husband of Frederick's sister Margaret. When he again refused to attend the 1235 diet in Mainz, Emperor Frederick II finally ostracized him and gave permission to King Wenceslaus I of Bohemia to invade the Austrian lands.