In spring 644, when the Tang emissary to Goguryeo, Xiangli Xuanjiang (), returned from Goguryeo, indicating that the Yeon Gaesomun, the Goguryeo general who then controlled the political scene there, was unwilling to stop his attacks against Silla, then a Tang vassal, Li Shiji advocated an attack against Goguryeo, and Emperor Taizong agreed, despite opposition by other officials, including Chu Suiliang. Emperor Taizong, after several months of preparations, launched a two-pronged attack against Goguryeo in winter 644, with Li Shiji in charge of the land army containing 60,000 soldiers, heading toward Liaodong Peninsula, and with Zhang Liang in charge of the navy numbering 40,000 soldiers, heading directly toward the Goguryeo capital Pyongyang. Emperor Taizong himself trailed them.