Goguryeo–Yan War

The Goguryeo-Yan War occurred in the 4th and 5th centuries between Goguryeo and Yan. The Goguryeo expansion met temporary setbacks when in 342, Former Yan, of Xianbei ethnicity, attacked Goguryeo’s capital and captured it briefly, taking the body of King Micheon (the father of then-reigning King Gogugwon) and the queen dowager (King Gogugwon's mother) as collateral for Goguryeo's submission. However, by 409, the end of Former Yan's first successor state Later Yan, Goguryeo appears to have captured all territory east of the Liao River previously held by Former Yan and Later Yan, and in 408 established peaceful relations with Gao Yun, the ruler of Later Yan's successor state Northern Yan, who was a descendant of Goguryeo's royal house. In 436, when Feng Hong, brother and successor of Gao Yun's successor Feng Ba, could not withstand Northern Wei attacks, he evacuated his people to Goguryeo territory. When he subsequently tried to rule part of Goguryeo territory as an independent state, however, he was killed by Goguryeo's King Jangsu. King Jangsu and his successors subsequently undertook the policy of maintaining peaceful relations with both China's Northern Dynasties (Northern Wei, Northern Qi, Northern Zhou, and Sui Dynasty) and Southern Dynasties (Liu Song, Southern Qi, Liang Dynasty, and Chen Dynasty), and there would not be major conflicts between Goguryeo and any Chinese state until Sui unified China by destroying Chen in 589.