Complex sentence: Kublai Khan realized the importance of hydraulic engineering, irrigation, and water transport, which he believed could help alleviate uprisings within the empire, and sent Guo to look at these aspects in the area between Dadu (now Beijing or Peking) and the Yellow River.
Split into simpler sentences: Kublai Khan realized the importance of hydraulic engineering, irrigation, and water transport, which he believed could help alleviate uprisings within the empire. Kublai sent Guo to look at these aspects in the area between Dadu (now Beijing or Peking) and the Yellow River.