The reign of the longevity king was the heyday of Koguryo. In 427, Koguryo moved its capital to Pyongyang, marking the shift of Koguryo's expansion direction from the east of Liaohe River in China to the Korean Peninsula.
In 427, the capital of Longevity King was in the inner city of Northeast China. Later, in order to avoid the threat of the Northern Wei Dynasty and consolidate its power on the Korean Peninsula, it moved its capital to Pyongyang City (that is, Sheng Da Mountain City and Anhe Miyagi City, six or seven kilometers northeast of Pyongyang, North Korea). After moving the capital to Pyongyang, we strengthened our control over Baekje and Silla. The Longevity King continued the expansion policy of King Tai Hao, which made the country win a complete victory.
During Luanhua period, northern China was divided into sixteen countries. Hou Yan, located in Liaoning, was finally destroyed by the Feng brothers in 408 because of his perennial fighting with Wang. The Han Dynasty established Beiyan by replacing Houyan with Feng Ba. But compared with Xianbei Northern Wei Dynasty, which unified northern China, Beiyan was no match for the Northern Wei Dynasty at all. Beiyan then sought an alliance with Goguryeo to compete with the Northern Wei Dynasty. After the death of Houyan, Koguryo took the opportunity to occupy western Liaoning occupied by Beiyan.
By the end of the Longevity King, Koguryo's population had increased to 90,000, and its territory had expanded unprecedentedly. Its southern Xinjiang is connected with Baekje and Silla from Yashan Bay via Niaoling and Zhuling to Pinghai, and extends to the banks of Datong River, Zainingjiang River, Linjin River and Hanjiang River in North Korea today, which is the heyday of Koguryo. According to Shu Wei? Koguryo Biography records that "when the number of households is twice that of Wei San before, the land is two thousand miles from east to west and one thousand miles from north to south". That is, it borders the Sea of Japan in the east, the Yellow Sea in the west, the Hanjiang River Basin in the south and the Liaohe River in the north. It is one of the most powerful kingdoms in Northeast Asia. At this time, Goguryeo shocked the Central Plains and stood up against the Central Committee.
In 475, the longevity king attacked Baekje from both land and sea. King Geru was unprepared for this. As a result, the longevity king easily captured the capital of Baekje, executed King Gallo and burned the Baekje Palace. Baekje was forced to move its capital to Jinxiong. In this war, Koguryo won the Hanjiang River Basin, a strategic place on the Korean Peninsula. Baekje occupied the Korean peninsula for nearly 500 years before it became a pole. After Baekje lost this area, it basically lost control of the Korean Peninsula.
After successfully defeating Baekje, Longevity King targeted Silla. King Changshou also built a stone tablet in Chungcheongbuk-do Chungcheongbuk-do, South Korea, to praise King Tai Hao and his achievements, and took this tablet as the boundary tablet between Koguryo and Baekje and Silla.
In 49 1 year, Emperor Xiaowen of the Northern Wei Dynasty conferred the title of Longevity King as a cycling general, a teacher, the founding duke of Liaodong County, and King Koguryo.
The longevity king reigned for more than 70 years and lived nearly a hundred years. After his death, Sun Wen succeeded to his throne.