Balhae’s First Embassy to Japan

King Mu of Balhae sent his first embassy to Japan; his letter declared that Balhae had recovered the old lands of Goguryeo and kept the customs of Buyeo.

Facing Tang and Silla, King Mu sought ties with Japan. His letter said that Balhae "has restored the old lands of Goryeo (Goguryeo) and keeps the customs of Buyeo". Later King Mun styled himself "King of Goryeo" in letters to Japan — evidence that Balhae saw itself as Goguryeo’s successor.

Balhae and Japan exchanged envoys for nearly two centuries along the "Japan Road" across the East Sea from the Eastern Capital.