The Boshin War, sometimes known as the Japanese Civil War, was a civil war in Japan fought from 1868 to 1869 between forces of the ruling Tokugawa shogunate and a clique seeking to seize political power in the name of Imperial Court.

The war was founded in dissatisfaction among many nobles and young samurai with the shogunate's handling of foreigners following the opening of Japan during the prior decade. Increasing Western influence in the economy led to a decline similar to that of other Asian countries at the time. An alliance of western samurai, particularly the domains of Chōshū, Satsuma and Tosa, and court officials secured control of the Imperial Court and influenced the young Emperor Meiji. Tokugawa Yoshinobu, the sitting shōgun, realizing the futility of his situation, abdicated political power to the emperor. Yoshinobu had hoped that by doing this, the House of Tokugawa could be preserved and participate in the future government.

However, military movements by imperial forces, partisan violence in Edo, and an imperial decree promoted by Satsuma and Chōshū abolishing the House of Tokugawa led Yoshinobu to launch a military campaign to seize the emperor's court in Kyoto. The military tide rapidly turned in favour of the smaller but relatively modernized imperial faction, and, after a series of battles culminating in the surrender of Edo, Yoshinobu personally surrendered. Those loyal to the Tokugawa retreated to northern Honshū and later to Hokkaidō, where they founded the Republic of Ezo. Defeat at the Battle of Hakodate broke this last holdout and left imperial rule supreme throughout the whole of Japan, completing the military phase of the Meiji Restoration.

Around 69,000 men were mobilized during the conflict, and of these about 8,200 were killed. In the end, the victorious imperial faction abandoned its objective of expelling foreigners from Japan and instead adopted a policy of continued modernization with an eye to eventual renegotiation of the unequal treaties with the Western powers. Due to the persistence of Saigō Takamori, a prominent leader of the imperial faction, the Tokugawa loyalists were shown clemency, and many former shogunate leaders and samurai were later given positions of responsibility under the new government.

When the Boshin War began, Japan was already modernizing, following the same course of advancement as that of the industrialized Western nations. Since Western nations, especially the United Kingdom and France, were deeply involved in the country's politics, the installation of Imperial power added more turbulence to the conflict. Over time, the war has been romanticized as a "bloodless revolution", as the number of casualties was small relative to the size of Japan's population. However, conflicts soon emerged between the western samurai and the modernists in the imperial faction, which led to the bloodier Satsuma Rebellion.