Castles During the Edo Period
The Sengoku Period came to a halt in 1615 when Tokugawa Ieyasu unified all of Japan under one government. After more than a century of war Tokugawa reigned in a peace of more than 250 years called the Edo Period. Even though an extended period of peace was established, castles still remained an important symbol of authority.
Under the Tokugawa regime each province was required to have one castle and no province could have more than one. As a result, some provinces with no castles were forced to build essentially useless castles. Other provinces had to tear down sometimes historically important castles to prevent having more than one in the province. This law, known as ikkoku ichijoo, also required daimyo to get permission from the Tokugawa governemnt to build, rebuild or renovate any castle. See the history of Hiroshima-jo for an account of what happened to one daimyo who rebuilt his castle without permission. During the Edo period there were approximately 170 castles throughout Japan.
Edo Period (1615-1868) History
The Edo Period was the period of the Tokugawa shoguns. At the end of the Sengoku Period, Tokugawa Ieyasu usurped power from the other daimyo and was granted the status of Shogun. Whether their policies were good or bad, Ieyasu and his descendents reigned in an era of over 250 years of peace in Japan. The first few Tokugawa shoguns went to great lengths to insure their dominance over the other daimyo throughout Japan.
The Tokugawa strategically placed their allies in territories that could keep watch over other daimyo who weren't Tokugawa allies from the Battle of Sekigahara. They also forced all of the daimyo to spend half of their time in Edo (Tokyo) which helped the Tokugawa to keep a close watch over their activities. These pilgrimages back and forth between Edo and their home territories placed great financial burdens on the daimyo which was also a part of the Tokugawa master plan.
The Tokugawa enforced strict social reforms too. They created a rigid caste system of samurai, peasants and merchants. The samurai were the only ones allowed to carry weapons and no one could change caste. They officially banned Christianity and closed Japan to the outside world. Only the Dutch and Chinese were allowed to trade with Japan and that was in a few closely monitored ports only. The Edo Period is also known as the sakoku jidai, the period of isolation.
During the two and a half centuries of peace, merchants who were supposedly at the bottom of the caste system prospered while the samurai fell into ruin. Since there were no more wars the samurai could not hone their skills and over time they lost most of their once cherished abilities. Towards the end of the Edo Period, many samurai didn't even carry real swords anymore. Many unfulfilled samurai turned to the arts to occupy their time and the Edo period saw a flourishing of art unparalleled in Japanese history.
Various internal and external influences led to an overthrow of the Tokugawa government in 1868.