Siege of Ansi Fortress

Date: October 13, 645 • Location: Haicheng, China

This milestone marked the outbreak and beginning of this historic period, which spanned 645–668.

Goguryeo–Tang War: Led by Emperor Taizong, the Tang army was forced to abandon a siege of Ansi Fortress.

The Goguryeo–Tang War occurred from 645 to 668 and was fought between Goguryeo and the Tang dynasty. During the course of the war, the two sides allied with various other states. Goguryeo successfully repulsed the invading Tang armies during the first Tang invasions of 645–648. After conquering Baekje in 660, Tang and Silla armies invaded Goguryeo from the north and south in 661, but were forced to withdraw in 662. In 666, Yŏn Kaesomun died and Goguryeo became plagued by violent dissension, numerous defections, and widespread demoralization. The Tang–Silla alliance mounted a fresh invasion in the following year, aided by the defector Yŏn Namsaeng. In late 668, exhausted from numerous military attacks and suffering from internal political chaos, Goguryeo and the remnants of Baekje army succumbed to the numerically superior armies of the Tang dynasty and Silla.