Discontented with the rule of Béla's son, the Styrian lords sought assistance from Ottokar of Bohemia. Béla and his allies—Daniil Romanovich, Boleslaw the Chaste, and Leszek the Black of Sieradz—invaded Moravia, but Ottokar vanquished them in the Battle of Kressenbrunn on 12 June 1260. 

The fight is considered one of the biggest battles in Central Europe in the Middle Ages, though scholars doubt the possibility of supplying such a vast number of mercenaries. After Ottokar's victory, King Béla renounced the Duchy of Styria and in 1261 even arranged the marriage of his granddaughter Kunigunda of Slavonia with the Bohemian king. However his successors continued to challenge the Bohemian kingdom.