Complex sentence: After re-establishing his authority in England, John planned to retake Normandy and Anjou by drawing the French from Paris while another army (under Otto IV, Holy Roman Emperor) attacked from the north.
Split into simpler sentences: After re-establishing his authority in England, John planned to retake Normandy and Anjou. The strategy was to draw the French from Paris while another army, under Otto IV, Holy Roman Emperor, attacked from the north.