Goguryeo reached its zenith in the 6th century. After this, however, it began a steady decline. Anjang was assassinated, and succeeded by his brother Anwon, during whose reign aristocratic factionalism increased. A political schism deepened as two factions advocated different princes for succession, until the eight-year-old Yang-won was finally crowned. But the power struggle was never resolved definitively, as renegade magistrates with private armies appointed themselves de facto rulers of their areas of control.

Taking advantage of Goguryeo's internal struggle, a nomadic group called the Tuchueh attacked Goguryeo's northern castles in the 550s and conquered some of Goguryeo's northern lands. Weakening Goguryeo even more, as civil war continued among feudal lords over royal succession, Baekje and Silla allied to attack Goguryeo from the south in 551.