Goryeo–Khitan War

The Goryeo–Khitan War were a series of 10th- and 11th-century invasions of Korea's Goryeo Dynasty by the Khitan Liao Dynasty near the present-day border between China and North Korea. It resulted in the defeat of Liao Dynasty.

Background
During the Three Kingdoms of Korea period, Goguryeo occupied the northern Korean Peninsula and parts of Manchuria and inner Mongolia. With Goguryeo's fall in 668, Silla unified the Three Kingdoms, while northern parts of Goguryeo territory were briefly occupied by Silla's ally Tang Dynasty China. A former Goguryeo general revived Goguryeo's Manchurian territory as the new kingdom of Balhae.

Right after the fall of Goguryeo, Turkic peoples (called Göktürks) were divided and eventually driven out from most of Central Asia by the Tang Dynasty. Another Turkic tribe, the Uyghurs, replaced the Göktürks but their control was not very strong.

As Balhae, the Uyghur and the Tang Dynasty weakened, the Khitan people, a nomadic confederation located in Manchuria and eastern Mongolia, grew stronger and began to expand their territory. Following Tang's fall in 907, China experienced a long period of civil war.

In 911, threatened by Khitan expansion, Balhae sought assistance from the declining Silla of the Korean Peninsula. Records stated that Balhae also requested help from Silla's successor dynasty Goryeo during the Later Three Kingdoms.

In 916, the Liao Dynasty was founded by the Khitan chief Yelü Abaoji, replacing the Uyghurs as the dominant power of present-day Mongolia.

Goryeo-Khitan relations
On the Korean Peninsula, Silla was succeeded by Goryeo in 918. The Khitan in 926 destroyed Balhae, and many of Balhae's ruling class moved south and joined the newly founded Goryeo Dynasty.

The Khitan took control of 16 Chinese provinces south of the Great Wall for helping the foundation of the short-lived Later Jin Dynasty (936-947), which ruled only a small part of China.

In 922, the Khitan leader Yelü Abaoji sent horses and camels to Goryeo as gifts of friendship. However, when Balhae fell to the Khitan a few years later, King Taejo embraced refugees from Balhae and pursued a policy of northern expansion (possibly enabled by the absence of a fellow Korean kingdom in what was once Goguryeo territory). In 942, the Khitan sent another 50 camels to Goryeo, but this time Taejo refused the gift, exiled the envoy to an island, and had the camels starved to death.

Succeeding Goryeo rulers continued the anti-Khitan policy. Jeongjong raised an army of 300,000 to defend against the Khitan. Gwangjong built fortresses along the northwest, and aggressively developed the military fortifications of present-day Pyongan and Hamgyong provinces.

Liao's expansion
In 962, Gwangjong of Goryeo allied with Song Dynasty in central China and pursued a northern expansion policy. Additionally, some Balhae refugees had formed a small state called Jeong-an Kingdom in mid-Yalu River region and allied with Song and Goryeo against the Khitan.

The Khitan eventually regained internal stability under the strong leadership of Emperor Shengzong, who sought to counter regional isolation. After conquering Jeongan-guk in 986 and attacking Jurchen tribes in lower Yalu in 991, the Khitans initiated attacks against Goryeo.

First Invasion
In 993, the Khitan invaded Goryeo's northwest border with 60,000 troops. The Khitan withdrew and ceded territory to the east of the Yalu River when Goryeo agreed to end its alliance with Song China. However, Goryeo continued to communicate with Song, having strengthened its position by building fortresses in the newly gained northern territories.

Second Invasion
The Khitan attacked again during an internal Goryeo power struggle. King Hyeonjong was forced to flee the capital temporarily, but Goryeo repulsed the Khitan attack. Finally, Khitan forces withdrew.

Third Invasion
When Goryeo continued to refuse to submit or return the northern territories, the Khitan attacked once more. Goryeo generals, including Gang Gam-chan, were able to inflict heavy losses on the Khitan army in the Battle of Kwiju. The Khitan withdrew without achieving their demands, and the two nations signed a peace treaty.