隋書
According to the "Book of Sui", Silla and Baekje greatly valued relations with the Kofun-period Wa and the Korean kingdoms made diplomatic efforts to maintain their good standing with the Japanese. The "Book of Song" reported that a Chinese emperor appointed the five kings of Wa in 451 to supervise military Affairs of Wa, Silla, Imna, Gara, Jinhan and Mahan.