Khitans under General Xiao Sunning had invaded…

Khitans under General Xiao Sunning had invaded Goryeo in 993, but retreated after truce negotiations with minister Seo Hui of Goryeo, establishing friendly relations between the two nations.

In 1004, Khitans invaded Song China.

Chinese forces were terribly defeated, and the Song dynasty had been forced to pay tribute to the Liao emperor.

However, the tension between Goryeo and Liao had created another war.

In 1009, General Gang Jo of Goryeo had led a coup against King Mokjong, killing the king and establishing military rule.

In 1010, the alliance had been broken and Liao had attacked Korea for General Gang's treason.

Also, Khitans claim six garrison settlements east of the Yalu River, which Goryeo had claimed as its territory in truce negotiations during 993.

The Goryeoans fought fiercely but were defeated.

However, the Goryeo king had managed to retain his claim on the six garrison settlements.

The Khitans had retreated from the peninsula, with no great prize for the war, but they have not given up their hope of gaining the six garrison settlements and making Goryeo pay tribute.

Beginning in the summer of 1018, the Khitans construct a bridge across the Yalu River, and the Khitan army invades Goryeo for the third time with one hundred thousand troops.

General Gang Gam-chan orders the Heunghaejin stream to be blocked until the Khitans begin to cross it; when the Khitans are mid-way across, he orders that the dam be destroyed so that the water will drown much of the Khitan army.

The damage is great, and General Gang leads a massive attack that annihilates many of the Khitan troops.