Britannica Sources used in this answer

How large was Goguryeo at the height of its power?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Map of the Korean Peninsula highlighted in orange, showing North Korea in the north and South Korea in the south. The peninsula is bordered by China and Russia to the north, the Yellow Sea to the west, the East Sea (Sea of Japan) to the east, and Japan across the sea to the southeast. A small inset globe at the top left shows the peninsula's location in East Asia. — Korea Map of the Korean Peninsula, indicating northern and southern regions.

At the height of its power, Goguryeo was the largest of the three ancient kingdoms of Korea. Its territory expanded significantly during the reigns of King Gwanggaeto (391–412) and King Jangsu (413–491).

During this peak period, the kingdom’s rule encompassed the entire northern half of the Korean peninsula, the Liaodong Peninsula, and a considerable portion of Manchuria in what is now China.1