Tokyo was settled by Japanese much later than the Yamato plain around Nara. However, it is believed to have been the largest human settlement in Japan during the neolithic era, prior to the establishment of the Yamato government. As one of Japan's three largest alluvial plains, the Kanto area is ideal for wet rice culture and during the early Heian period as the population grew and demand for farmland increased, large numbers of Japanese migrated to the area where modern Tokyo is situated. These people were mostly independent from the central government and the rise of the warrior class, which caused the end of the Heian era had its roots in the independent manorial lords who settled in Eastern Japan.