Jinsa, the younger brother of Chimnyu, had ascended to the throne because the heir, later King Asin, was too young, according to the Samguk Sagi.

According to the Japanese Nihon Shoki, however, he usurped the throne by force.

Jinsa has ordered numerous attacks against Goguryeo, which is expanding into Baekje territory from the north.

In the year 386, he commands all men above the age of fifteen living in Cheongmongnyeong (present-day Kaesong) to move north and west to defend the borders.

He sends the noble Jin Gamo to attack the Goguryeo Dogon Castle, which is conquered.

Goguryeo, surrounded by the powerful forces of Baekje to its south and west, is therefore inclined to avoid conflict with its peninsular neighbor while cultivating constructive relations with the Xianbei and Rouran in order to defend itself from future invasions, and even the possible destruction of its state.

Gwanggaeto succeeds his father, King Gogukyang, upon his death in 391.

Immediately upon being crowned king of Goguryeo, Gwanggaeto grants himself the title Emperor Yeongnak, affirming himself as equal to the rulers of China and the king of Baekje.

He now begins to rebuild and retrain Goguryeo's cavalry units and naval fleet.

Gwanggaeto’s military forces see action in 392 against Baekje.

With Gwanggaeto in personal command, Goguryeo attacks Baekje with fifty thousand cavalry, taking ten walled cities along the two countries' mutual border.