The Shinsengumi (新選組, "Newly Selected Corps") was a small, elite group of swordsmen that was organized by commoners and low rank samurai, commissioned by the bakufu (military government) during Japan's Bakumatsu period (late Tokugawa shogunate) in 1863.

One long-standing line of political opinion was sonnō jōi (meaning, "revere the emperor, expel the barbarians").

[4]: 168 The squad's nominal commander was the hatamoto Matsudaira Katamori, and their leader was Kiyokawa Hachirō, a rōnin from Shōnai Domain.

The Rōshigumi's mission was to protect Tokugawa Iemochi, the 14th shōgun, during an important trip to Kyoto to meet with the Emperor Kōmei.

Tokugawa Iemochi, the head of the military government, the bakufu, had been invited to discuss how Japan should enact the recent imperial edict calling for the expulsion of foreigners.

[6]: 186 Although the Rōshigumi was funded by the Tokugawa bakufu, the leader Kiyokawa Hachirō and others had strong loyalties to the emperor and planned to gather other rōnin in Kyoto to police the city from insurgents.

The Shinsengumi submitted a letter to the Aizu clan, another powerful group who supported the Tokugawa regime, requesting permission to police Kyoto.

On October 19, 1863, Niimi Nishiki, a member of the Serizawa faction was forced by Yamanami Keisuke and Hijikata Toshizō to commit seppuku for breaking regulations.

They were the first samurai group of the Tokugawa era to allow those from non-samurai classes (farmers and merchants, for example) to join.

The code of the Shinsengumi, famously created by Hijikata Toshizō, included five articles, prohibiting deviation from the samurai code (bushido), leaving the Shinsengumi, raising money privately, taking part in others' litigation, and engaging in private fights.

Following the orders of the Shinsengumi commander Serizawa Kamo, the standard uniform consisted of the haori and hakama over a kimono, with a white cord called a tasuki crossed over the chest and tied in the back.

[10] In 1867, when Tokugawa Yoshinobu withdrew from Kyoto, the Shinsengumi left peacefully under the supervision of the wakadoshiyori, Nagai Naoyuki.

Right after the Battle of Kōshū-Katsunuma, Nagakura Shinpachi, Harada Sanosuke and some of the members left the Kōyō Chinbutai after disagreements with long-time comrades Kondo and Hijikata and later formed a new unit Seiheitai with a former Tokugawa retainer Haga Gidou as its commander.

Kondō was declared guilty of participation in the assassination of Sakamoto Ryōma on April 30, 1868 and was beheaded three weeks later at the Itabashi execution grounds on May 17, 1868.

[5]: 217–230 The Shinsengumi numbers decreased to around one hundred in this period and they fought on despite the fall of Edo and clear defeat of Tokugawa.

[4] In the Battle of Miyako Bay on 6 May 1869, Hijikata led a daring but doomed raid to steal the imperial warship Kōtetsu, in the early morning, from the Kaiten warship, a number of oppositionists, including Nomura Risaburō, managed to board the ship, but were soon mowed down by its Gatling gun.

A remaining group of survivors, under the last commander Sōma Kazue, who had been under Nagai Naoyuki's supervision at Benten Daiba, surrendered three days later on June 23, (lunar calendar May 14), 1869, marked the end of the Shinsengumi.

[5]: 246  The forces of the Republic of Ezo would later surrender on June 27, (lunar calendar May 18), 1869, which marked the end of the Boshin War.

At that time, the Japanese considered the Meiji Restoration a great achievement and regarded the current system centered around Satsuma and Choshu as just.

Ryōtarō Shiba's novel "Moeyo Ken" (1964) gained popularity, spreading empathy towards the way of life of the Shinsengumi.