King Munjamyeong was the grandson of King Jangsu. His father, Joda, had been named crown prince by King Jangsu, who outlived his son. As the prince died young, King Jangsu raised his grandson as his successor. When the king died in 491, his grandson came to the throne.
By the time Munjamyeong became king, Goguryeo had gained a large territory spanning at least 400-thousand square kilometers. The entire Korean Peninsula today covers 220-thousand square kilometers, so we can only imagine the colossal amount of land ruled by the ancient kingdom.
To reign over the extensive territory inherited by his predecessors, King Munjamyeong focused on diplomacy. Just as his grandfather King Jangsu did, Munjamyeong maintained friendly relations with various Chinese dynasties and tribes to stabilize regional diplomacy. The king maintained a subtle balance between the strong Chinese kingdom of Northern Wei and the Liang Dynasty, which was an emerging power. To its south, on the other hand, the king continued to confront two southern kingdoms, Baekje and Silla, which formed an alliance to jointly block the strong forces from the northern kingdom of Goguryeo. But the situation was much different from the period of his predecessors. It was not easy to attack the allied forces as they tenaciously resisted. The southwestern Baekje kingdom even invaded Goguryeo on several occasions. But the king attacked Baekje in 512 to capture its castles and take 1,000 people captive. Following the crushing defeat, Baekje could no longer invade Goguryeo. Historical records say that Goguryeo accepted the surrender of the royal family of the Buyeo state in 494 when the northern kingdom was toppled by the Mohe tribe.
In 498, the king built the Geumgang-sa Buddhist temple to promote Buddhism.
During his 28-year reign, the king managed to fend off the allied forces in the south and maintain his territory to sustain the golden period of Goguryeo. But the kingdom’s power was not as strong as it once was under the two predecessors. After his death in 519, aristocrats engaged in a fierce power struggle and it seems the next king was assassinated in that process. Due to the internal chaos and instability, royal power began to weaken drastically. It would be fair to say that King Munjamyeong was the last monarch of Goguryeo’s glory days.