The battle started on 27 January 1868 (or fourth year of Keiō, first month, 3rd day, according to the lunar calendar), when the forces of the shogunate and the allied forces of Chōshū, Satsuma and Tosa Domains clashed near Fushimi, a town near Kyoto, the sacred capital, and fighting progressed to the Toba road leading to Osaka, with the initial rout of the Satsuma from Fushimi.

[3][4][full citation needed] However, while Yoshinobu's resignation created a nominal void at the highest level of government, his apparatus of state continued to exist.

The Tokugawa family also retained a very large domain around Edo, valued at more than 2 million Koku, a prospect hard-liners from Satsuma and Chōshū found intolerable.

[citation needed] The battle started when shogunate forces moved in the direction of Kyoto to deliver a letter from Yoshinobu, warning the Emperor of the intrigues plotted by Satsuma and the court nobles who supported it, such as Iwakura Tomomi.

[11] According to historian Conrad Totman: "In terms of army organization and weaponry, the four main protagonists probably rank in this order: Chōshū was best; Bakufu infantry was next; Satsuma was next; and Aizu and most liege vassal forces were last.

The Shogun also relied on troops supplied by allied domains, which were not necessarily as advanced in terms of military equipment and methods, making up an army that had both modern and outdated elements.

[16] At around 17:00, the shogunate vanguard, made up largely of about 400 men of the Mimawarigumi, armed with pikes and some firearms, under Sasaki Tadasaburo, approached a Satsuma-manned barrier post at the Koeda Bridge (小枝橋), Toba (located in what is now part of Minami-ku, Kyoto).

On 28 January, Iwakura Tomomi gave Saigō Takamori and Ōkubo Toshimichi orders obtained from Emperor Meiji proclaiming Tokugawa Yoshinobu and his followers to be enemies of the court, authorizing their suppression by military force, and granting use of the Imperial brocade banners.

[21] These brocade banners were prepared beforehand, having been made by Ōkubo Toshimichi a few months previously, and stored in Chōshū domain and in the Satsuma Kyoto residence until an appropriate opportunity presented itself.

[22] In addition, Imperial Prince Yoshiaki, a young man of 22, who had lived as a Buddhist monk at the monzeki temple of Ninna-ji was named nominal commander in chief of the army.

The daimyō of Yodo maintained his gates closed despite the supplication of the retreating army, thus denying them a major means of defense, forcing them to flee as far as Osaka castle.

At Osaka Castle, Tokugawa Yoshinobu gathered his advisors and military leaders to plan strategy and, to boost morale, advised that he would personally take to the field as commander of bakufu forces.

That evening however, he slipped away from Osaka Castle accompanied by the daimyōs of Aizu and Kuwana to escape back to Edo on the shogunate warship Kaiyō Maru.

[24] French advisors Jules Brunet and Cazeneuve, who were present at the battle, left Osaka and returned to Edo on 12 January, together with Enomoto Takeaki on board the Fujiyama.

The prestige and morale of the Tokugawa bakufu was seriously weakened, and many daimyōs who had remained neutral now declared in favor of the Emperor and offered military support to prove their new loyalties.

Even more significantly, the ill-conceived attempt by Tokugawa Yoshinobu to regain control silenced elements within the new imperial government who favored a peaceful resolution to the conflict.