Goguryeo (traditionally 37 BCE–668 CE) was the northernmost and most militarized of the Three Kingdoms of early Korea, a fortress state that ruled much of the northern Korean peninsula and southern Manchuria. It is remembered for repelling enormous Chinese invasions before falling to a Silla–Tang alliance, and its heritage is now contested between Korea and China, which advance rival historical claims to a kingdom that predated both modern nations.
In 612, the Sui emperor threw one of the largest armies the ancient world had yet assembled at a single mountain kingdom. Goguryeo's general Eulji Mundeok lured it deep, then loosed a dammed river across its line of retreat. Of some 300,000 men who had marched toward the capital, a Chinese history says a few thousand reached home. Within six years the Sui dynasty itself had collapsed.