In feudal Japan, individual military and citizens groups were primarily responsible for self-defense until the unification of Japan by Tokugawa Ieyasu in 1603. During the Edo period (1603–1868), the Tokugawa shogunate formed a centralized feudal government. Samurai warriors who once protected Japan from foreign enemies and fought each other for supremacy became the new police and internal security force. Their new job would be to ensure civil peace, which they accomplished for over 250 years.