Kublai Khan became the supreme leader (a title for their leader) of the Mongol Empire and moved his capital to Beijing. He was at war with the southern Chinese Song Dynasty. The Mongol Empire lost some of its battles. The first time it lost a battle with Kublai Khan as the leader was in Palestine when fighting the Mamluks of Egypt. The Empire also lost in the Caucasus. The Mamluks were led by their new sultan Baibars. The Mamluks were soon were more in control in the Middle East because they took control of a number of crusader states and also stopped the Mongol attacks from happening as much. The Empire of Nicaea took control of Constantinople and also the Latin Empire so it again became the Byzantine Empire.