In the second year of his reign, Gogukyang sent 40,000 troops to attack the Chinese state of
Later Yan in the
Liaodong Peninsula. The Goguryeo army captured Liaodong and
Xuantu, and took 10,000 prisoners. In 386, the prince Go Dam-deok, the later King
Gwanggaeto the Great, was designated heir to the throne. It is said Dam-deok served his father in battlefields since he was teenager. Goguryeo attacked the southern Korean kingdom of
Baekje in 386, which returned the attacks in 389 and 390. In the spring of 391, Goguryeo signed a treaty of friendship with King
Naemul of
Silla, another of the Three Kingdoms, and received Naemul's nephew
Kim Sil-seong as a hostage. == Death and succession==