When Ottokar followed Removing his father as King of Bohemia in 1253 , Béla , distrustful of his rising Cause_change_of_position_on_a_scale power , claimed Statement the Styrian duchy .

However , in 1260 the conflict Hostile_encounter rekindled Recovering , after the Styrian nobility had revolted Change_of_leadership against the Árpáds and Ottokar campaigned Military_operation the duchy .

Historians estimate Statement that up to half of Hungary 's then population of 2,000,000 were victims Death of the Mongol invasion Ottokar 's troops consisted of Bohemian-Moravian , German , Polish , Carinthian , Carniolan and Styrian forces , while Bela 's huge army gathered Come_together Hungarian , Slovak , Cuman , Russian , Polish , Bulgarian , Wallachian , Ukrainian ( Galician ) , Slavonian , Croatian , Bosnian , Serbian , Pecheneg and Szekler contingents .