The was a series of battles undertaken by the Tokugawa shogunate against the Toyotomi clan, and ending in that clan's destruction. Divided into two stages (Winter Campaign and Summer Campaign), and lasting from 1614 to 1615, the siege put an end to the last major armed opposition to the shogunate's establishment. The end of the conflict is sometimes called the , because the era name was changed from Keichō to Genna immediately following the siege.
The siege was begun on November 19, when Ieyasu led three thousand men across the Kizu River, destroying the fort there. A week later, he attacked the village of Imafuku with 1,500 men, against a defending force of 600. With the aid of a squad wielding arquebuses, the shogunal forces claimed another victory. Several more small forts and villages were attacked before the siege on Osaka Castle itself began on December 4.
The Sanada-maru was an earthwork barbican defended by Sanada Yukimura and 7,000 men, on behalf of the Toyotomi. The Shogun's armies were repeatedly repelled, and Sanada and his men launched a number of attacks against the siege lines, breaking through three times. Ieyasu then resorted to artillery, bringing in 300 cannon, as well as men to dig under the walls. On January 22, the Winter Siege was ended, with Toyotomi Hideyori pledging to not rise in rebellion, and allowing the moat of Osaka castle to be filled in.
In April 1615, Ieyasu received word that Toyotomi Hideyori was gathering even more troops than in the previous November, and that he was trying to stop the filling of the moat. Toyotomi forces (often called the Western Army) began to attack contingents of the Shogun's forces (the Eastern Army) near Osaka. Commanded by Ban Danemon, they raided Wakayama Castle, a coastal fortress belonging to Asano Nagaakira, an ally of the Shogun, on April 29. Asano's men sallied forth from the castle, attacking the invaders, and driving them off. By early June, the Eastern army had arrived, before Hideyori managed to secure any land to use against them. At the battle of Dōmyōji, on June 2, 2,600 of his men encountered 23,000 of the Eastern Army. Hideyori's commander at the battle, Gotō Matabei, attempted to retreat into the fog, but the battle was lost and he was killed. After this, Tokugawa forces intercepted those of Toyotomi general Sanada Yukimura at Honta-Ryo. Sanada tried to force a battle with Date Masamune, but Date retainer Katakura Shigenaga retreated since his troops were exhausted; Sanada's forces followed suit.
The same night, Chōsokabe Morichika and Tōdō Takatora battled at Yao. Another battle took place at Wakae around the same time, between Kimura Shigenari and Ii Naotaka. Chōsokabe's forces achieved victory, but Kimura Shigenari was defected by the left wing of Ii Naotaka's army. The main Tokugawa forces moved to assist Todo Takatora after Shigenari's death, and Chōsokabe withdrew for the time being.
After another series of shogunate victories on the outskirts of Osaka, the Summer Campaign came to a head at the battle of Tennoji. Hideyori planned a hammer-and-anvil operation, in which 55,000 men would attack the center of the Eastern Army, while a second force, of 16,500 men, would flank them from the rear. Another contingent waited in reserve. Ieyasu's army was led by his son, the Shogun Tokugawa Hidetada, and numbered around 155,000. They moved in four parallel lines, prepared to make flanking maneuvers of their own. Mistakes on both sides nearly ruined the battle, as Hideyori's ronin split off from the main group, and Hidetada's reserve force moved up without orders from the main force. In the end, however, Hideyori's commander Sanada Yukimura was killed, destroying the morale of the Western Army. The smaller force led directly by Hideyori sallied forth from Osaka Castle too late, and was chased right back into the castle by the advancing enemies; there was no time to set up a proper defense of the castle, and it was soon ablaze, and being pummeled by artillery fire. Hideyori committed seppuku, and the final major uprising against Tokugawa rule was put to an end, leaving the shogunate unchallenged for another 250 or so years.
History indicates that the legendary swordsman Miyamoto Musashi participated in the battle on the Toyotomi side. It is unknown how he fared but what is known is that Musashi was spared by Ieyasu for unknown reasons.
The bakufu obtained 650,000 koku at Osaka and started rebuilding Osaka Castle. Osaka was then made a han (feudal domain), and given to Matsudaira Tadayoshi. In 1619, however, the shogunate replaced Osaka Domain with Osaka Jodai, placed under the command of a bugyō who served the shogunate directly; like many of Japan's other major cities, Osaka was for the remainder of the Edo period not part of a han under the control of a daimyō. A few daimyō including Naitō Nobumasa (Takatsuki Castle, Settsu Province 20,000 koku) and Mizuno Katsushige (Yamato Koriyama, Yamato Province 60,000 koku) moved to Osaka.
The Toyotomi clan was then disbanded. Tadanao was the first to arrive at Osaka Castle. He turned down the land reward, but instead received chaki. The lords of the castle over time thus were Ashikaga Yoshimasa, followed by Oda Nobunaga, Tokugawa Ieyasu, Toyotomi Hideyoshi, Ukita Hideie, and finally Hatsuhana Katatsuki.
After the fall of the castle, the shogunate announced laws including Ikkuni Ichijōrei (one province can contain only one castle) and Bukeshohatto (or called Law of Buke, which limits each daimyō to own only one castle and obey the castle restrictions). The shogunate's permission had to be obtained prior to any castle construction or repair from then on. Many castles were also forced to be destroyed as a result of compliance with this law.
Despite finally uniting Japan, Ieyasu's health was failing. During the one year campaign against the Toyotomi clan and its allies, he received wounds that significantly shortened his life. Roughly one year later on June 1 1616, Tokugawa Ieyasu, the third and last of the great unifiers, died at the age of 75, leaving the shogunate to his descendants.