Political and economic relations between Korea and Japan are suspended completely following the war.

Ieyasu, the most powerful of the five regents, forges alliances with various daimyo, especially those who had no love for Hideyoshi.

With the death in 1599 of Toshiie, the oldest and most respected of the regents, Ieyasu leads an army to Fushimi and takes over Osaka Castle, the residence of Hideyori.

This angers the three remaining regents and plans are made on all sides for war.

Opposition to Ieyasu centers upon Ishida Mitsunari, a powerful daimyo but not one of the regents.

Ishida plots Ieyasu's death and news of this plot reached some of Ieyasu's generals.

They attempt to kill Ishida but he flees and gains protection from Ieyasu himself.

Although it is unclear why Ieyasu would protect a powerful enemy from his own men, Ieyasu, a master strategist, may have concluded that he would be better off with Ishida leading the enemy army rather than one of the regents, who would have more legitimacy.

The shogun seeks to establish a powerful and stable regime under the rule of his own clan; only the Toyotomi, led by the late Hideyoshi’s son Hideyori and based at Osaka, remain as an obstacle to this goal.

The Toyotomi clan in 1614 rebuilds Osaka Castle, which Hideyori as a minor daimyo while his mother Yodo plots a Toyotomi return to power.

At the same time, the head of the clan sponsors the rebuilding of Hōkō-ji in Kyoto.

These temple renovations include the casting a great bronze bell, with an inscription that reads "May the state be peaceful and prosperous; In the East it greets the pale moon, and in the West bids farewell to the setting sun.".

The shogunate, which has its power base in the eastern provinces, interprets this as an insult, and tensions begin to grow between the Tokugawa and the Toyotomi clan, which only increase when Hideyori begins to gather a force of ronin and enemies of the shogunate in Osaka.

Ieyasu, despite having passed the title of Shogun on to his son in 1605, nevertheless maintains significant influence, and by November decides not to let this force grow any larger, leading one hundred and sixty-four thousand men to Osaka (the count does not include the troops of Shimazu Tadatsune, an ally of the Toyotomi cause who nevertheless does not send troops to Osaka).

The siege begins on November 19, when Ieyasu leads three thousand men across the Kizu River, destroying the fort there.

He attacks the village of Imafuku a week later with fifteen hundred men, against a defending force of six hundred.

With the aid of a squad wielding arquebuses, the shogunal forces claim another victory.

Several more small forts and villages are attacked before the siege on Osaka Castle itself begins on December 4.

Bands of Christian samurai support Ieyasu's enemies at the Battle of Osaka.

The Sanada-maru is an earthwork barbican defended by Sanada Yukimura and seven thousand men, on behalf of the Toyotomi.

The Shogun's armies are repeatedly repelled, and Sanada and his men launch a number of attacks against the siege lines, breaking through three times.

Ieyasu then resorts to artillery, which include seventeen imported European cannons and domestic wrought iron cannon, as well as men to dig under the walls.

The Winter Siege is ended on January 22, with Toyotomi Hideyori pledging to not rise in rebellion, and agreeing to allow the destruction of the castle’s outer moat, but Ieyasu’s envoys instead destroy both the outer and inner moats, leaving the castle defenseless.

Ieyasu receives word in April 1615 that Toyotomi Hideyori is gathering even more troops than in the previous November, and that he is trying to stop the filling of the moat.

Toyotomi forces (often called the Western Army) begin to attack contingents of the Shogun's forces (the Eastern Army) near Osaka.

Commanded by Ban Danemon, they raid Wakayama Castle, a coastal fortress belonging to Asano Nagaakira, an ally of the Shogun, on April 29.

Asano's men sally forth from the castle, attacking the invaders, and driving them off.

The Eastern army arrives by early June, before Hideyori manages to secure any land to use against them.

Six hundred of his men encounter twenty-three thousand of the Eastern Army on June 2 at the battle of Dōmyōji.

Hideyori's commander at the battle, Gotō Matabei, attempts to retreat into the fog, but the battle is lost and he is killed.

After this, Tokugawa forces intercept those of Toyotomi general Sanada Yukimura at Honta-Ryo.

Sanada tries to force a battle with Date Masamune, but Date retainer Katakura Shigenaga retreats since his troops are exhausted; Sanada's forces follow suit.

The same night, Chōsokabe Morichika and Tōdō Takatora battle at Yao.

Another battle takes place at Wakae around the same time, between Kimura Shigenari and Ii Naotaka.

Chōsokabe's forces achieve victory, but Kimura Shigenari is defected by the left wing of Ii Naotaka's army.

The main Tokugawa forces move to assist Todo Takatora after Shigenari's death, and Chōsokabe withdraws for the time being.

After another series of shogunate victories on the outskirts of Osaka, the Summer Campaign comes to a head at the battle of Tennoji.

Hideyori plans a hammer-and-anvil operation, in which fifty-five thousand men would attack the center of the Eastern Army, while a second force, of sixteen thousand five hundred men, would flank them from the rear.

Another contingent waits in reserve.

Ieyasu's army is led by his son, the Shogun Tokugawa Hidetada, and numbers around one hundred and fifty-five thousand.

They move in four parallel lines, prepared to make flanking maneuvers of their own.

Mistakes on both sides nearly ruin the battle, as Hideyori's ronin split off from the main group, and Hidetada's reserve force moves up without orders from the main force.

In the end, however, Hideyori's commander Sanada Yukimura is killed, destroying the morale of the Western Army.

The smaller force led directly by Hideyori sallies forth from Osaka Castle too late, and is chased right back into the castle by the advancing enemies; there is no time to set up a proper defense of the castle, and it is soon ablaze, and being pummeled by artillery fire.

Hideyori commits seppuku, and the final major uprising against Tokugawa rule is put to an end, leaving the shogunate unchallenged for another two hundred and fifty or so years.

After the fall of the castle, the shogunate announces 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 has to be obtained prior to any castle construction or repair from this point on.

Many castles are also forced to be destroyed as a result of compliance with this law.