Defeating Goguryeo had been an obsession with Emperor Taizong, and after his death in 649, his son Emperor Gaozong continued his ambition. Upon the suggestion of Kim Chunchu, the Silla–Tang alliance first conquered Baekje in 660 to break up the Goguryeo–Baekje alliance, and then turned its full attention to Goguryeo. However, Emperor Gaozong, too, was unable to defeat Goguryeo led by Yeon Gaesomun; one of Yeon Gaesomun's most notable victories came in 662 at the "Battle of Sasu" (蛇水), where he annihilated the Tang forces and killed the invading general Pang Xiaotai (龐孝泰) and all 13 of his sons. Hence, while Yeon Gaesomun was alive, Tang could not defeat Goguryeo.