Little direct evidence remains from the reign of King Gwanggaeto the Great in Korea's early Three Kingdoms period (57 BCE - 668 CE). Some surviving Chinese documents mention the Korean kingdoms of Koguryeo, Silla and Baekje, and there are carved stone monuments with information about a few specific rulers or events.
The most impressive of the monuments is Gwanggaeto's Stele, a 7-meter tall (23 foot) piece of granite carved in memory of Gwanggaeto at his son's instruction in 414 CE. Because the stele stands in what is now Jilin Province, China, it has been the source of much historical rancor between modern-day Koreans and Chinese.
Gwanggaeto was born in 374 CE to King Gogukyang of Koguryeo and an unknown consort. His birth name was Go Dam-deok; the boy was officially made crown prince in 386.
Gwanggaeto became king in 391 when his father died. The 17-year-old designated himself Supreme King Yeongnak (meaning "Eternal Peace"), and immediately went to war.
Gwanggaeto's Military Conquests:
In 392, Gwanggaeto led his army against the neighboring kingdom of Baekje. Goguryeo's 50,000 mounted warriors conquered about a dozen cities along the border with Baekje, but were unable to fight their way deeper into the kingdom. Baekje's King Asin led two counter-attacks against Goguryeo in 393 and 394, but both were repulsed.
In 395, Gwanggaeto invaded again and took control of a considerable portion of Baekje. A surprise naval attack on Baekje in 396 resulted in complete defeat for King Asin.
Baekje was down but not out. It allied itself with the Japanese and the southern Gaya Kingdoms to attack Silla, the third of the Three Kingdoms.
Silla appealed to Goguryeo for help, and Gwanggaeto answered the call with 50,000 soldiers, who defeated all of the other parties involved. Silla, Baekje and Gaya all submitted and became tributaries of Goguryeo; the Japanese went home.
When the Xianbei people of northwest China invaded Goguryeo, also in 400, Gwanggaeto retaliated. He went on to conquer their entire kingdom by 402. In 404, he also seized the whole Liaodong Peninsula; the Xianbei launched two major invasions of Goguryeo, but were unable to retake their former territory.
Gwanggaeto soon conquered Inner Mongolia, far to the west of Goguryeo. He then turned his attention northward, driving deep into what is now Siberia to take the ethnically Korean kingdom of Dongbuyeo with its 64 walled cities, as well as a number of Sumo Mohe and Ainu settlements.
Gwanggaeto's Early Death:
In 413, the 39-year-old King of a vastly expanded Goguryeo died suddenly of an unnamed disease. He had unified most of the Korean Peninsula under his control, and extended his power to Mongolia in the west and the Siberian coast of the Pacific in the northeast. This kingdom was the largest ever built by a Korean ruler.
Greater Goguryeo survived its builder by about 50 years before coming apart again. Nevertheless, Gwanggaeto became one of just two Korean monarchs honored with the title "The Great" - the other being Sejong the Great (1397-1450 CE) of the Joseon Dynasty.
Gwanggaeto's Legacy and Stele:
In 414, King Jangsu of Goguryeo erected the mighty Gwanggaeto Stele in honor of his father's memory. The posthumous name "Gwanggaeto" means "Great Expander of the Realm." The 1800 Chinese characters inscribed into the granite tell the story of Goguryeo's history to that point, particularly Gwangaeto's reign.
Goguryeo fell in 668 CE, and the area around the stele changed hands frequently, as it was in the fracture line between settled Korean or Chinese peoples and nomadic peoples of the steppe. For much of the time after about 1000 CE, the region was under the Jurchen or Manchu people, who did not pay any notice to the stele.
Late in the 19th century, Japan, China and Russia began to fight over Manchuria, and a Chinese scholar discovered the stele under a thick layer of plant growth and dirt. As soon as the characters from all four sides were translated, China, Korea and Japan began to fight about what the words meant for their respective histories.
China resents the discovery of an ethnically Korean monument so far into what is now Chinese territory, and has tried to claim Goguryeo as its own. Japan is delighted that the stele seems to support their legends about early conquests on the Korean Peninsula, perhaps even that of Japan's Empress Jingu. Koreans (both North and South) bitterly oppose the Sinification of Goguryeo, and refuse to admit the possibility that the Japanese could have conquered Silla and/or Baekje.
Given the scarcity of other evidence about this period, we may never know the entire truth about some of these claims and counter-claims. Certainly, the controversy continues to this day. It is a shame that Gwanggaeto himself cannot speak to us across the ages, and clarify his legacy.