In 1273 Ottokar became embroiled in a dispute with the Swabian count Rudolf of Habsburg over his election as King of the Romans. The next year Rudolf and the Imperial Diet of Nuremberg demanded that all fiefs acquired during the "interregnum" after the death of Emperor Frederick II of Hohenstaufen in 1250 were to revert to the Imperial crown, a demand which would have applied to Austria, Carinthia and Carniola. Ottokar refused, but was eventually put under Imperial ban in 1276 and forced to cede the lands, only retaining his Kingdom of Bohemia with Moravia. Two years later he was defeated and killed in the Battle on the Marchfeld. Under Habsburg rule, Carniola became a frontier against Venice in the southwest, while its eastern border with Hungary remained stable.