Upon the conquest of the Principality of Vladimir by the Mongols in 1238, its reigning Prince, Yuri II Vsevolodovich, was killed in the Battle of the Sit River; his younger brother, Yaroslav II Vsevolodovich, requested from, and received from, the Mongol khan installation as the new Prince. As Prince, he assigned the duchy of Novgorod to his son Alexander. However, while traveling in 1245 to the Mongol capital Karakorum in Central Asia, Yaroslav died. When in 1248 Alexander and his older brother Andrey II Yaroslavich also traveled to Karakorum to attend upon the Great Khan, Andrei returned with the award of the Grand Principality of Vladimir and Alexander the nominal lordship of Kiev. Once Möngke became the new Great Khan in 1251, all the Russian princes were obliged to travel to Sarai on the Volga, the capital of the Golden Horde, to be affirmed in their duchies, but Andrei refused to go. Thanks to his friendship with Sartaq Khan, the subsequent invasion by the Mongol Golden Horde saw Andrei exiled to Sweden and Alexander installed as the Grand Prince of Vladimir (i.e., the supreme Russian ruler) in 1252. Alexander faithfully supported Mongol rule within his domains. In 1259 he led an army to the city of Novgorod and forced it to pay tribute it had previously refused to the Golden Horde. Returning in 1263 from one of his frequent visits to the Horde, Alexander died in the town of Gorodets-on-the-Volga on his way back from Sarai. Prior to his death, he took monastic vows and was given the religious name of Alexis.