The Kofun period (古墳時代 - Kofun-jidai, lit. "period of ancient mound/tomb"?), beginning around AD 250, is named after the large burial mounds (kofun) that appeared at the time. The Kofun period saw the establishment of strong military states centered around powerful clans, and the establishment of the dominant Yamato polity centered in the Yamato and Kawachi provinces, from the 3rd century to the 7th century, origin of the Japanese imperial lineage. The polity, suppressing the clans and acquiring agricultural lands, maintained a strong influence in the western part of Japan. Japan started to send tributes to Imperial China in the 5th century. In the Chinese history records, the polity was called Wa and its five kings were recorded. Based upon the Chinese model, they developed a central administration and an imperial court system and its society was organized into occupation groups.
Close relationships between the Three Kingdoms of Korea and Japan began during the middle of this period, around the end of the 4th century. According to a controversial part on the Gwanggaeto Stele, Japan actively participated with large armies on the Korean Peninsula during the late 4th and early 5th centuries. According to the Book of Song, of the Liu Song Dynasty, the Liu-Song emperor formally awarded the king of Yamato, which he considered to be his vassal, the title of military sovereignty over Silla and the Gaya confederacy.[11] However, others dispute this theory, claiming there is no evidence of Japanese rule in Gaya or any other part of Korea.[12][13][14] The Samguk Sagi (Chronicles of the Three Kingdoms) recorded Baekje and Silla sent their princes as hostages to the Wa to ensure military support; King Asin of Baekje sent his son Jeonji in 397[15] and King Silseong of Silla sent his son in 402.[16] This interpretation is complicated by the claim that the rulers of Japan could be of Korean descent.[17][18]