In winter 820, major events that tested Emperor Muzong's abilities to keep these circuits under control came. Wang Chengzong the military governor of Chengde, whose family had controlled Chengde since his grandfather Wang Wujun and whose forces Emperor Xianzong was unable to defeat (although Wang Chengzong himself eventually became apprehensive of Emperor Xianzong's might and submitted anyway), died. With Wang Chengzong having sent his sons Wang Zhigan () and Wang Zhixin () to Chang'an to serve as hostages in order to show his submission to the imperial government, his subordinates, who wanted to keep Chengde independent from the imperial government, supported Wang Chengzong's brother Wang Chengyuan to succeed him. Wang Chengyuan pretended to accept their support, but declared his loyalty to the imperial government and secretly petitioned Emperor Muzong to replace him.