The exact cause of Genghis Khan's death is unclear, but it is believed that he died in August 1227 from injuries sustained during a fall from his horse. According to legend, Genghis Khan's biggest regret was that he was never able to conquer the kingdom of Xi Xia, which was located in what is now northwestern China. Despite several attempts, Genghis Khan was never able to defeat the Xi Xia army, and he is said to have been deeply disappointed by this failure.