The Yayoi people were separate people from their predecessors, the Jomon people.  It is likely they entered Japan from Korea.  They brought with them agricultural capabilities such as rice and irrigation.  These technologies revolutionized agriculture in Japan, not only improving quality of life, but extending it.  This agricultural technology also allowed for more permanent settling across Japan.  They also brought iron, and metal working became widespread across Japan.  In general, trade became more prevalent, and cities begin to accumulate wealth (relatively speaking).

The Yayoi are known for their jar burials.  Queen Himiko/Pimiko* emerges near the end of the Yayoi era as a unifier of Japan, as well as being recognized as a separate entity by China. She represents the emergence of the Yamamoto State.

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*The character for hi/pi is ひ・ぴ and the record of the Queen leave this spelling unclear.