Complex sentence: The Mongol armies in Europe broke camp and went back to Mongolia to select a new Khan maintaining the tradition since the death of Genghis Khan which by Ogodei's death Europe is spared from further carnage.
Split into simpler sentences: The Mongol armies in Europe broke camp and went back to Mongolia to select a new Khan maintaining the tradition by since the death of Genghis Khan. By Ogodei's death Europe is spared from further carnage.