By the end of 644, the Eastern Tujue people, who were not whole-heartedly supportive of Ashina Simo in the first place, collapsed in light of Xueyantuo threat, fleeing back to Tang territory, and were again settled there. Ashina Simo also went back to Tang and again became a Tang general, ending Tang's attempt to recreate Eastern Tujue as a vassal state. This caused Emperor Taizong to be displeased, and when Yi'nan subsequently sent an emissary to offer tribute to Emperor Taizong, who was at that time deeply into preparation to attack Goguryeo, Emperor Taizong responded, "Go back and tell your khan: My son and I are now about to attack Goguryeo. If he thinks that he can take advantage of this, he is welcome to come!" Yi'nan, fearful of Emperor Taizong's anger, sent another emissary to apologize and offering to assist in the operation against Goguryeo, an offer that Emperor Taizong declined. In 645, after Emperor Taizong had defeated the main Goguryeo forces at Mount Zhubi (), near the fortress of Anshi (, in modern Anshan, Liaoning), Goguryeo's mangniji (regent) Yeon Gaesomun requested that Yi'nan attack Tang, offering great tributes to him if he did. Yi'nan, fearful of Tang power, did not do so. (However, Emperor Taizong was eventually forced to abandon the campaign anyway after being stymied in his siege of Anshi.)