by the Mongols have also faced steppe tactics successfully before. A significant number of important castles and towns in Hungary had also resisted the formidable and infamous Mongol siege tactics. John Keegan thought that Europeans had an advantage due to more food surpluses enabling better campaigns, and larger horses. Some historians believe that the reason for Batu's stopping at the Mohi River was that he never intended to advance further. He had made the new Rus' conquests secure for the years to come, and when the Great Khan died and Batu rushed back to Mongolia to put in his claim for power, it ended his westward expansion. Subutai's recall at the same time left the Mongol armies without their spiritual head and primary strategist. Batu Khan was not able to resume his plans for conquest to the "Great Sea" (the Atlantic Ocean) until 1255, after the turmoil after Ögedei's death had finally subsided with the election of Möngke Khan as Great Khan. Though he was capable of invading Western Europe, he was no longer interested . Mongol infighting From 1241 to 1248 a state of almost open warfare existed between Batu, son of Jochi, and Güyük, son of Ögedei. The Mongol Empire was ruled by a regency under Ögedei's widow Töregene Khatun, whose only goal was to secure the Great Khanate for her son, Güyük. There was so much bitterness between the two branches of the family that when Güyük died in 1248, he was on his way to confront Batu to force him to accept his authority. Batu also had problems in his last years with the Principality of Halych-Volhynia, whose ruler, Danylo of Halych, adopted a policy of confronting the Golden Horde and defeated some Mongol assaults in 1254. He was finally defeated in 1259, when Berke ruled the Horde. Batu Khan was unable to turn his army west until 1255, after Möngke had become Great Khan in 1251, and he had repaired his relations with the Great Khanate. However, as he prepared to finish the invasion of Europe, he died. His son did not live long enough to implement his father and Subutai's plan to invade Europe, and with his death, Batu's younger brother Berke became Khan of the Kipchak Khanate. Berke was not interested in invading Europe as much as stopping his cousin Hulagu Khan from ravaging the Holy Land. Berke had converted to Islam and