Tokugawa Ieyasu served as regent for Hideyoshi's son Toyotomi Hideyori and used his position to gain political and military support. When open war broke out, Ieyasu defeated rival clans in the Battle of Sekigahara in 1600. He was appointed ''shōgun'' by Emperor Go-Yōzei in 1603 and established the Tokugawa shogunate at Edo (modern Tokyo). The shogunate enacted measures including ''buke shohatto'', as a code of conduct to control the autonomous ''daimyōs'', and in 1639 the isolationist ''sakoku'' ("closed country") policy that spanned the two and a half centuries of tenuous political unity known as the Edo period (1603–1868). Modern Japan's economic growth began in this period, resulting in roads and water transportation routes, as well as financial instruments such as futures contracts, banking and insurance of the Osaka rice brokers. The study of Western sciences (''rangaku'') continued through contact with the Dutch enclave in Nagasaki. The Edo period gave rise to ''kokugaku'' ("national studies"), the study of Japan by the Japanese.