Buyeo Abang, the eldest son of Baekje's fifteenth ruler Chimnyu, had ascended to the throne after the death of Chimnyu’s brother, the sixteenth king Jinsa, whom he is said to have killed.

The Goguryeo offensive infuriates Asin, who subsequently plans a counteroffensive against Gwanggaeto, a plan he is forced to abandon when his invasion force is defeated by Goguryeo 393.

King Asin again attacks Goguryeo in 394, and is again defeated.

Baekje has begun to crumble politically after several heavy defeats, and Asin’s leadership comes under doubt.

Asin loses to Goguryeo again in 395, and he is eventually pushed back to a front along the Han River, where Wiryeseong, Baekje's capital city, is located in the southern part of modern day Seoul.

Gwanggaeto himself attacks and conquers Biryu, a small nation located in central Manchuria, during a campaign against Baekje in 395. (Its exact location is not known but it was not very far from the Songhua River.)

Gwanggaeto leads his huge fleet in an assault on Wiryesong in 396, approaching by sea and river.

Asin,expecting a ground invasion, is caught with his defenses down.

Gwanggaeto's forces burn about 58 walled fortresses under Baekje control and defeat the forces of Asin, who surrenders to Gwanggaeto, even handing over his brother as a captive as a condition for maintaining his own rule over Baekje.

Gwanggaeto has finally gained superiority over its longtime rival Baekje on the Korean peninsula.

Japan’s Kofun period, which had begun around 250, is named after the large burial mounds that had appeared at the time.

Illustrated by an animistic culture that exists prior to the introduction of Buddhism, the Kofun period sees the establishment of strong military states centered around powerful clans, and the establishment of a dominant polity centered in the Yamato area from the third century on: the Yamato Court, origin of the Japanese imperial lineage.

The Yamato Court, suppressing the clans and acquiring agricultural lands, maintains a strong influence in the western part of Japan (the Asuka region).

Based upon the Chinese model, they have developed a central administration and an imperial court system and society is organized into occupation groups.

Several proto-state formations rival one another, possibly representing different ethnic backgrounds.

Close relationships between the Three Kingdoms of Korea and Japan begin during the middle of this period, around the end of the fourth century.

(According to the Gwanggaeto Stele, Japan actively participates with large armies on the Korean Peninsula during the late fourth and early fifth centuries.

According to the Book of Song, of the Liu Song Dynasty, the Chinese emperor appointed the king of Yamato to also be ruler of Silla, Baekje, and the Gaya confederacy.

According to the Samguk Sagi (Chronicles of the Three Kingdoms), Baekje and Silla sent their princes as hostages to the Yamato court to ensure military support; King Asin of Baekje sent his son Jeonji in 397.)

Silla submits to Goguryeo in 399 for protection from raids from Baekjae.

Many consider this loose unification under Goguryeo to have been the first and only true unification of the Three Kingdoms.

Many peasants are said to have fled to Silla during another round of conscription by Asin of Baekje for the battles against Goguryeo in 399.

King Asin of Baekje attacks Silla in 403, whence many of his subjects had fled in 399 to avoid conscription.