Complex sentence: Although the Mongols killed Henry and destroyed his forces, their advance into Europe was halted when they turned back to attend to the election of a new Khagan (Grand Khan) following the death in the same year of Ögedei Khan.
Split into simpler sentences: Although the Mongols killed Henry and destroyed his forces, their advance into Europe was halted. The battle coincided with the election of a new Khagan (Grand Khan) following the death in the same year of Ögedei Khan.