The usual explanation is that Ashikaga Takauji had turned on the Hojo and went to Go-Daigo's side because he expected to be rewarded handsomely in the fall of the Kamakura Shogunate. He was actually rewarded handsomely, but he wanted to be named the next Shogun. Go-Daigo instead named his son.

Meanwhile Go-Daigo's attempt to restore Imperial rule made quite a mess of things, making the court incredibly unpopular with both old foes and supporters during the fight against the Hojo. So the Ashikaga took this chance to, once again, rebel when they were sent to crush a rebellion.