 However, under attacks by Li Shimin and Li Shentong, Xu's territory continued to shrink.Li Shimin then returned to the Tang capital Chang'an, but left Li Shentong, Li Shiji, and Ren Gui (任瓌) in the region to continue to attack Xu.By spring 623, Tang forces were putting Xu's capital at Yan under siege, and Xu's soldiers were surrendering in droves.