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.[1] Samurai warriors who once protected Japan from foreign enemies and fought each other for supremacy became the new police and internal security force.[2] Their new job would be to ensure civil peace, which they accomplished for over 250 years.[3]