During his early reign, Jangsu dedicated much of his efforts toward stabilizing an empire that had experienced great and sudden growth as a direct result of his father's conquests.

During Gwanggaeto's time, Goguryeo invaded Later Yan and conquered Liaoning,[21] but when Jangsu came to the throne, the chaos in northern China was coming to an end.

The Northern Wei government was upset by Jangsu's actions but had to keep peace with Goguryeo to continue its war against Liu Song and the Rouran Khaganate.

Under the reign of Emperor Xiaowen alone, 41 emissaries were sent,[29] but the frequency started to drop since Jangsu continued to keep hospitality with Qi.

[24] Confronted with harsh attacks from Goguryeo into the southern region of the Korean peninsula, Baekje and Silla found their survival through marriage alliances, beginning in 433.

The alliance between Baekje and Silla lasted more than a century and was the primary reason why Goguryeo was unable to conquer the entire peninsula.

[30] Gaya found itself in a precarious situation due to its geographical disadvantage of being sandwiched by Baekje and Silla, and ultimately could not develop into an advanced nation.

[32][33] In response, Jangsu secretly planned to attack Baekje, which despite its losses against Gwanggaeto the Great, still held a significant power base in the Korean peninsula.

In order to disarm Baekje, he sent a Buddhist monk named Dorim,[2] who went to Gaero's court with the secret objective of corrupting the country.

Henceforth, Baekje had no choice but to move its capital to mountainous Ungjin (present-day Gongju), 80 miles to the south, which provided a natural protection for the devastated kingdom.

[2][33] The war gave Goguryeo more or less total control of the Han River valley, the region essential to commercial and military power in the Korean peninsula.

[37] To secure the allegiance of his de facto protectorate, Jangsu demanded the younger brother of King Nulji of Silla to become a political hostage.

Age of Empires: World Domination, a mobile game produced in collaboration with series owner Microsoft,[42] includes Jangsu as a selectable hero of the Korean civilization.