Emperor Taizong of Tang used Yeon Gaesomun's murder of King Yeongnyu of Goguryeo as the pretext for his campaign and started preparations for an invasion force in 644. General Li Shiji commanded an army of 60,000 Tang soldiers and an undisclosed number of tribal forces which gathered at Youzhou. Emperor Taizong commanded an armored cavalry of 10,000 strong.
Emperor Taizong of Tang leveraged Yeon Gaesomun's murder of King Yeongnyu of Goguryeo as a pretext for his military campaign and began mobilizing troops in 644. General Li Shiji oversaw an army consisting of 60,000 Tang soldiers and tribal forces that converged on Youzhou. Emperor Taizong led a formidable armored cavalry force of 10,000 warriors.