Ieyasu's father, Matsudaira Hirotada, was a minor local warlord based at Okazaki Castle who controlled a portion of the Tōkaidō highway linking Kyoto with the eastern provinces.

[26][page needed][28] Some historians believe that these actions provoked the pro-Imagawa faction, including the Sakurai and Okusa Matsudaira families, which led to the simultaneous uprising against Ieyasu in the following year.

[29] During this period, the Matsudaira clan faced a threat from the Ikkō-ikki movement, where peasants banded together with militant monks under the Jōdo Shinshū sect, and rejected the traditional feudal social order.

[48] Several reports from Mikawa Monogatari, Nobunaga Koki, Tokugawa Jikki, and a supplement from Ietada Nikki recorded that Ieyasu and his forces also participated in Oda's punitive campaign against Asakura where they fought and captured the Mount Tenzutsu castle.

[53][46] The battle was a major defeat, but in the interest of maintaining the appearance of a dignified withdrawal, Ieyasu brazenly ordered the men in his castle to light torches, sound drums, and leave the gates open, to properly receive the returning warriors.

[53] This error allowed a band of Tokugawa soldiers to raid the camp in the ensuing hours, further upsetting the already disoriented Takeda army, and ultimately resulting in Shingen's decision to call off the offensive altogether.

[58] In April 1575, Ōga Yashirō, a deputy governor of over 20 villages in Oku district of Mikawa under Matsudaira Nobuyasu,[59] was arrested by Ōkubo Tadayo and paraded around Hamamatsu Castle.

Tokugawa Ieyasu heard that Nobunaga had been killed by Akechi Mitsuhide while in Hirakata, Osaka, but at the time, he had only a few companions with him,[78] notably Sakai Tadatsugu, Ii Naomasa, and Honda Tadakatsu, Sakakibara Yasumasa and some others.

[93][i][96][97][98][99] At first, the Hōjō clan, who ruled the Kantō region, led an army of 55,000 men to invade the Shinano Province through Usui,[93] as they aimed to prevent a Tokugawa incursion of Kai.

Okabe Masatsuna, a member of the Suruga clan samurai who once served under Baba Nobuharu,[107] took the initiative to defend the rear of Tadatsugu's army from the enemy charges and repelled them.

The next day, Ieyasu also sent a letter to Masatsuna instructing him to begin the construction of a castle at Shimoyama, Minobu Town in the Kai Kawachi domain, the former base of Anayama Nobutada, one of Tokugawa's retainers who was killed by outlaws during his escape after the Honnō-ji Incident.

[118] Ieyasu managed to recruit more samurai clans who had formerly served under various Takeda generals such as Ichijō Nobutatsu, Yamagata Masakage, and Hara Masatane with the assistance of Ii Naomasa.

[135] At the same time, a Tokugawa army detachment from the Iga Province commanded by Hattori Hanzō invaded the Saku District, where they were aided by local Shinano samurai warriors from the Tsugane clan led by Öbi Sukemitsu.

In the Saku district, he only had Yoda Nobushige who was struggling by himself in guerilla warfare against the Hōjō, as the bulk of new Tokugawa supporters such as the Takekawa and Tsugane clans of Kai also suffered from a shortage of provisions while the number of anti-Hōjō forces continued to grow.

[105] Between November 1582 to January 1583, in conjunction with the main battles at Wakamiko and Kurokoma which were still ongoing, Komai Masanao worked together with Torii Mototada and Ii Naomasa, along with Suwa Yoritada, who had joined the Tokugawa rank, to attack the Chikuma District which was controlled by Ogasawara Sadayoshi.

However, both of them were repeatedly beaten on the field at Nagakute by Mizuno Katsunari,[179] and later, Ii Naomasa, caused the Toyotomi forces to suffer heavy losses with both Tsuneoki and Nagayoshi killed in action.

In response, Hideyoshi sent a punitive expedition with an army 30,000 strong led by Ieyasu Tokugawa, Toyotomi Hidetsugu, Date Masamune, Ishida Mitsunari, Ōtani Yoshitsugu, Gamō Ujisato, Uesugi Kagekatsu, Satake Yoshishige, and Maeda Toshiie, in order to pacify the rebellion.

Historians saw this step as aimed at bringing order to the newly subdued population of the area, while also guarding the eastern domains from any influence or threat from the Satomi clan which had not yet submitted to Toyotomi rule at that time.

[211][212] Ieyasu, who at that time was also busy suppressing rebellions with his main commanders, including Sakakibara Yasumasa, Ii Naomasa, and Honda Tadakatsu, arrived at Iwatesawa, Tamazukuri district, Mutsu (modern day Iwadeyama, Miyagi Prefecture) on August 18, where he camped until October and led the troops.

[215][211][203] The rebellions were suppressed by June 20, with Waga Yoshitada being slain in battle,[216] while Hienuki Hirotada was sentenced to "Kaieki law" which stated that his and his clan's status and rights as samurai were stripped.

The Tokugawa clan samurai didn't take part in this campaign, as Hideyoshi had ordered the eastern provinces' daimyo including Ieyasu, Uesugi Kagekatsu, and Date Masamune to maintain logistical support for the war effort in Nagoya Castle.

Later, though still in early 1593, Ieyasu himself was summoned to Hideyoshi's court in Nagoya (in Kyushu, not the similarly spelled city in Owari Province) as a military advisor and was given command of troops meant as reserves for the Korean campaign.

This change in the pre-Sekigahara power structure, became pivotal as Ieyasu turned his attention towards Kansai; and at the same time, other ambitious (albeit ultimately unrealized) plans, such as the Tokugawa initiative establishing official relations with New Spain (modern-day Mexico), continued to unfold and advance.

There may have been several factors that contributed to his decision, including his desires to avoid being tied up in ceremonial duties, to make it harder for his enemies to attack his real power center, and to secure a smoother succession for his son.

Mitsunari viewed Terumoto, who had been raised in the comfortable and stable domains of the Mōri clan, as contrasting with the hardships Ieyasu faced during his childhood, who experienced instability in Mikawa province, where he spent much his youth as a hostage of other warlords which formed each leader's character into different ways.

Mitsunari viewed this contrast of leadership style as being reflected in the Sekigahara battle, where the indecisiveness of Terumoto cost the Western army greatly, while Ieyasu's bold decision and his willingness to take risks gave him the edge during the war.

[295] Tetsuo Owada personally praised how Ieyasu managed to be quickly accepted by the citizens of the Kantō region and his ability to rule there without unrest after he transferred there, by continuing the lenient tax policies of the Hōjō clan in order to gain sympathy.

[296] Hamada Koichiro from Himeji Dokkyo University has recorded that there is a systematic attempt of historiography studies in the aftermath of the Meiji Restoration to portray Ieyasu in a negative light as a "cunning old man" who used the temple's bell of Hokoji as casus belli to wage war against Hideyori.

[298] According to professor Watanabe Daimon, one of the biggest strengths of Ieyasu's policies was his benevolence towards his subordinates and his capability to forgive his enemies and even his own generals who betrayed him during the Mikawa Ikkō-ikki uprising.

Despite his personal devotion to Jōdo-shū, Ieyasu was not a strict sectarian, placing his secretary Denchōrō, a Rinzai Zen monk, in charge of all religious affairs in Japan, Buddhist and Shinto alike.