Although Ögedei Khan had granted permission to invade the remainder of Europe, all the way to the "Great Sea", the Atlantic Ocean, the Mongol advance stalled in East Europe early in 1242, the year after his death. Mongol propaganda would later attribute the drive's failure to his untimely demise necessitating Batu's withdrawal to personally participate in the election of Ögedei's successor. But Batu never in fact returned to Mongolia for such an election and a successor wouldn't be named until 1246. A likely reason the advance stalled and never regained momentum is that European fortifications posed a strategic problem that Mongol commanders were unable to surmount with the resources they had available.