Golden Age of King Geunchogo
King Geunchogo absorbed Mahan and attacked Goguryeo’s Pyongyang, opening Baekje’s golden age and trading by sea with Eastern Jin and Wa.

Geunchogo conquered the remnants of Mahan down to the south coast of Jeolla and extended his influence over Gaya. In the north he fought Goguryeo for Hwanghae, killing King Gogugwon in 371.
He opened relations with Eastern Jin and Wa; the Seven-Branched Sword kept at Isonokami Shrine in Japan is thought to have been sent by Baekje to the Wa king, though Korean and Japanese scholars differ on whether it was a royal gift or tribute. The scholar Go Heung compiled the history Seogi, and father-to-son succession took hold.