Gwanggaeto the Great was the nineteenth monarch of Goguryeo. Under Gwanggaeto, Goguryeo began a golden age, becoming a powerful empire and one of the great powers in East Asia. Gwanggaeto made enormous advances and conquests into: Western Manchuria against Khitan tribes; Inner Mongolia and the Maritime Province of Russia against numerous nations and tribes; and the Han River valley in central Korea to control over two-thirds of the Korean peninsula.

In regard to the Korean peninsula, Gwanggaeto defeated Baekje, the then most powerful of the Three Kingdoms of Korea, in 396, capturing the capital city of Wiryeseong in present-day Seoul. In 399, Silla, the southeastern kingdom of Korea, sought aid from Goguryeo due to incursions by Baekje troops and their Wa allies from the Japanese archipelago. Gwanggaeto dispatched 50,000 expeditionary troops, crushing his enemies and securing Silla as a de facto protectorate; he thus subdued the other Korean kingdoms and achieved a loose unification of the Korean peninsula under Goguryeo. In his western campaigns, he defeated the Xianbei of the Later Yan empire and conquered the Liaodong peninsula, regaining the ancient domain of Gojoseon.

Gwanggaeto's accomplishments are recorded on the Gwanggaeto Stele, erected in 414 at the supposed site of his tomb in Ji'an along the present-day China–North Korea border.