Daimyos were a key part of the Japanese feudal system, which was based on a hierarchical structure of lords and vassals. The daimyos were vassals of the shogun, who was the military dictator of Japan. The shogun relied on the daimyos to maintain order and to provide military support. In return, the shogun granted the daimyos land and other privileges.
The Middle Ages in Japan came to an end in the 16th century, when the country was reunified under the rule of the Tokugawa shogunate. The Tokugawa shoguns took many of the powers of the daimyos away, and they established a more centralized government. However, the daimyos still remained important figures in Japanese society and politics.