King Gwanggaeto the Great was undoubtedly the greatest conqueror in Korean history. Indeed, the prominent historical figure wrote a glorious history of military expedition, as indicated by his name Gwanggaeto, which literally means “great expander of territory.” The famous monarch governed Goguryeo from 391 to 413 when the kingdom was at the height of its political and military power. During his 22-year reign, the king expanded Goguryeo’s territory up north into Manchuria, which is now part of northeast China, and down south to the Hangang River that flows through Seoul today. The territory extended even further west to present-day Mongolia. In other words, under the king’s reign, Goguryeo controlled two-thirds of the Korean Peninsula, Manchuria, parts of Russia’s maritime province of Primorsky Krai and inner Mongolia. Except for the period of the fifth century and the later kingdom of Balhae, Korea had never before or since controlled such large territory.

Today, the king is one of only two rulers in Korea’s long history to be given the title of “great” after their names. The other one is King Sejong the Great of the Joseon Dynasty, who invented the Korean alphabet of Hangeul.

King Gwanggaeto the Great was born in 374 and came to the throne in 391 at the tender age of 17. At the time of his birth, Goguryeo was not very powerful. On the contrary, the southwestern neighboring state of Baekje defeated Goguryeo in major battles, even killing a king of Goguryeo. Upon ascending the throne, King Gwanggaeto unleashed a campaign of retaliation by attacking Baekje and taking ten castles there. Baekje launched counter-attacks several times, only to fail. After the repeated severe defeats, Baekje began to weaken politically. As a result, Goguryeo was able to expand its territory down south to the Hangang River and win over its longtime rival in the south.

In the year 400, another Korean kingdom of Silla in the southeast asked the strong Goguryeo to help fight off the alliance of Baekje, Japan and the Gaya Confederacy in the south. King Gwanggaeto sent 50-thousand troops and defeated the allied forces. Subsequently, Goguryeo wielded great influence upon Silla. The two southern states, namely, Baekje and Silla, were, in effect, vassal states of Goguryeo. Some historians consider this loose unification led by Goguryeo as the only true unification of the Three Kingdoms.

The king’s aggressive military expedition didn’t end there. He turned his eyes to the north to conquer the Chinese state of Later Yan and other tribes. Next time, I’ll talk more about the king’s phenomenal conquest and legacy.