Gwanggaeto the Great's reign (391-412 CE) marked the zenith of Goguryeo's power, transforming it into a dominant empire in Northeast Asia. Ascending the throne amidst a complex geopolitical landscape, with powerful neighbors like Baekje to the south, Silla and Gaya on the peninsula, and various nomadic tribes and Chinese dynasties (Later Yan) to the north, Gwanggaeto embarked on an ambitious program of territorial expansion. His military campaigns were swift and decisive, earning him the posthumous title "Gwanggaeto," meaning "broad opener of territory." By 412 CE, the year of his death, Gwanggaeto had dramatically reshaped the map. To the north, he pushed Goguryeo's borders deep into Manchuria, conquering Khitan and Mohe tribes and extending influence over the Later Yan dynasty. To the south, he launched devastating attacks against Baekje, capturing key fortresses and weakening its power. Most famously, in 400 CE, he responded to Silla's plea for aid against invading Wa (Japanese) forces, dispatching a massive army of 50,000 cavalry and infantry that decisively routed the invaders and solidified Goguryeo's suzerainty over Silla. This intervention is a crucial event recorded on his stele. The legacy of Gwanggaeto's achievements was monumental, establishing Goguryeo as the hegemon of the Korean Peninsula and a major player in East Asian politics. To commemorate his father's unparalleled accomplishments, King Jangsu, Gwanggaeto's son, erected the magnificent Gwanggaeto Stele in 414 CE near his tomb in Ji'an (modern-day China). This colossal monument, one of the largest inscribed steles in the world, details Gwanggaeto's divine lineage, his extensive military campaigns, and the establishment of administrative structures. It serves as an invaluable primary source for understanding early Korean history, though its inscription has been subject to intense scholarly debate, particularly concerning the interpretation of passages related to Wa and Silla, which has fueled historical controversies between Korea and Japan. The stele stands as a testament to a golden age of Korean power and a lasting historical puzzle.