The Yayoi people, arriving from the Asian mainland between 1,000 and 800 BCE,^[11] brought significant changes to the Japanese archipelago. They introduced new technologies like rice cultivation^[12] and metallurgy, initially imported from China and the Korean peninsula. Originating from northern Kyūshū, the Yayoi culture gradually supplanted the indigenous Jōmon people,^[13] also resulting in a small genetic admixture between the two. This period witnessed the introduction of other technologies such as weaving, silk production,^[14] new woodworking methods,^[11] glassmaking,^[11] and new architectural styles.^[15]

There is ongoing debate among scholars about whether these changes were primarily due to migration or cultural diffusion, although genetic and linguistic evidence tends to support the migration theory. Historian Hanihara Kazurō estimates that the annual immigrant influx ranged from 350 to 3,000 people.^[16] As a result of these developments, Japan's population surged, possibly increasing tenfold compared to the Jōmon period. By the end of the Yayoi period, the population is estimated to have been between 1 and 4 million.^[17] The skeletal remains from the late Jōmon period indicate deteriorating health standards, while Yayoi sites suggest improved nutrition and societal structures, including grain storehouses and military fortifications.^[11]

During the Yayoi era, tribes coalesced into various kingdoms. The Book of Han, published in 111 CE, mentions that Japan, referred to as Wa, was composed of one hundred kingdoms. By 240 CE, according to the Book of Wei,^[18] the kingdom of Yamatai, led by the female monarch Himiko, had gained prominence over the others. The exact location of Yamatai and other details about it are still a subject of debate among modern historians.