The last years of the fourteenth century were characterized by the increasing Turkish threat. This threat was not from the small Turkmen emirates that bordered Trebizond, but from the dynasty of the Osmanli, a new Turkish power emerging from western Anatolia that would soon consolidate the Ottoman Empire. Although their expansion was temporarily checked by Tamerlane at the Battle of Ankara in 1402, by the 1430s the Ottomans had recovered their fortunes, seizing large segments of Greece and finally capturing Constantinople itself on 29 May 1453. Manuel III (1390–1417), the second son and successor of Alexios III, had allied himself with Tamerlane, but the mighty conqueror soon left Anatolia, and the empire he had built crumbled with his death. His son Alexios IV (1417–1429) continued the tradition of political marriages by marrying two of his daughters to rulers of two neighboring Muslim empires: Jihan Shah, khan of the Kara Koyunlu, and Ali Beg, khan of the Ak Koyunlu. His eldest daughter Maria became the third wife of the Byzantine Emperor John VIII Palaiologos.