Complex sentence: After defeating Khwarazm in 1221, Genghis prepared his armies to punish Western Xia for their betrayal, and in 1225 he attacked with a force of approximately 180,000.
Split into simpler sentences: After defeating Khwarazm in 1221, Genghis prepared his armies to punish Western Xia for their betrayal. In 1225, Genghis attacked with a force of approximately 180,000.