 In 643, under attack by the Goguryeo–Baekje alliance, the Silla court dispatched Kim Chunchu to the Tang dynasty to request military assistance, leading to Emperor Taizong's campaign against Goguryeo.In 660, Goguryeo's ally, Baekje, fell to the Silla–Tang alliance; the victorious allies continued their assault on Goguryeo for the next eight years but could not defeat Yeon Gaesomun.However, Yeon Gaesomun died of a natural cause and civil war ensued among his three sons, leading the Silla–Tang alliance to launch a fresh invasion.