戊辰戦争と奥羽越列藩同盟：会津の運命Origins of Japan's Skewed Power Balance

In 1868, when the new government army, centering around the Satsuma, Choshu, and Tosa domains, emerged victorious in the Meiji Restoration, the newly established administration further expanded the turmoil. The largest battle that ensued was known as the Boshin War (戊辰戦争). Although initially framed as an internal conflict between the former shogunate forces and the new government army, it gradually escalated into a significant civil war, decisively shaping Japan’s future from the modern era onwards, and its effects continue to resonate deeply today. This article will outline the Boshin War, focusing particularly on the crucial Ouetsu Reppan Alliance (奥羽越列藩同盟).

In November 1867, at Nijo Castle in Kyoto, Yoshinobu Tokugawa, the 15th shogun of the Edo Shogunate, returned political authority to Emperor Meiji. However, just prior to this event in October, the Satsuma and Choshu domains, which had intensified secret maneuvers at the imperial court, began advocating for the military overthrow of the shogunate. They orchestrated preparations to legitimize their military coup by securing an imperial decree.

Utilizing the symbolic authority of the Emperor, their forces initiated a coup against the shogunate army. Following the shogunate army’s defeat at the Battle of Toba-Fushimi (鳥羽伏見の戦い) in January 1868, Yoshinobu Tokugawa, observing the eastward advance of the new government forces, relinquished Edo Castle, his central stronghold, unconditionally. This marked the collapse of the Edo Shogunate, ending approximately 260 years of the Edo period. Nevertheless, the new government army, intoxicated by its military strength, continued its offensive. After capturing Edo in the east, they proceeded to advance further northeast into the Tohoku region. This was because central elements of the former shogunate’s military power remained predominantly within the northeastern domains of Aizu (会津藩) and Shonai (庄内藩). Upon capturing Edo, the new government army regarded the Aizu and Shonai domains as its greatest adversaries and relentlessly advanced to eliminate them completely.

Alarmed by the new government’s aggressive military campaign to control Japan, the Aizu domain attempted to prevent the spread of war to the Tohoku region by formally expressing their willingness to surrender. However, the new government army imposed unrealistic surrender conditions: the handover of the domain lord Katamori Matsudaira, surrender of Aizu Castle, and the complete confiscation of Aizu’s territories. Naturally, these terms were unacceptable. Witnessing the arrogant posture of the new government army, the samurai of the Aizu domain resolved to resist fiercely. A significant underlying factor in this tension was the composition of the new government army itself, primarily formed from lower-ranking samurai of the Satsuma, Choshu, and Tosa domains. The Aizu domain, having held elite status throughout the Edo period, found it particularly intolerable that such lower-ranking samurai had seized power by relying on modern weaponry and brute force. Ultimately, the arrogance of the new government and Aizu’s determination to resist caused tension to ripple through other northeastern domains.

In May 1868, inspired by Aizu’s resolve and harboring growing resentment towards the new government’s aggression, the Sendai domain took the lead, convening 25 powerful domains from Tohoku and Echigo regions at Shiroishi Castle, a strategic fortress south of the Miyagi domain. They formed an alliance and petitioned directly to the Imperial Court, rather than the new government, for clemency towards the Aizu and Shonai domains. However, the Imperial Court, unable to defy the new government forces, ignored this plea. This rejection became the catalyst that unified all 31 domains from Tohoku and Echigo regions, openly declaring resistance against the new government army. Thus, the Ouetsu Reppan Alliance was established. Initially, the alliance aimed merely to rescind the order to punish Aizu, constituting a defensive cooperation. Gradually, however, it evolved to assert the independence of the various domains against the new government politically.

As a result, immediately following the struggle between the shogunate forces and the new government army during the Meiji Restoration, Japan became deeply divided. Nevertheless, significant internal issues plagued the alliance. Due to the vast geographical expanse of the allied territories, substantial cultural differences, and historical grievances deeply embedded among the domains, their objectives were not uniformly aligned. Moreover, as the military superiority of the new government became increasingly evident, some domains quickly switched allegiance, causing the alliance’s unity to rapidly deteriorate. Consequently, the cohesion of the alliance swiftly weakened, creating an overwhelmingly advantageous position for the new government forces.

Let us now consider why the Aizu domain held such significance. Geographically, the Aizu domain was situated at the strategic gateway to northeastern Japan and maintained an extensive territory throughout the Edo period. Among the fudai daimyo (hereditary retainers) of the Tokugawa Shogunate, Aizu consistently occupied a central position. The domain’s founder, Masayuki Hoshina, was the fourth son of Hidetada Tokugawa, the second Tokugawa shogun, and a half-brother of Iemitsu Tokugawa, the third shogun. After Iemitsu’s death, Masayuki served as regent and Tairo (大老) for the fourth shogun, thus becoming an immensely significant figure politically and holding close blood ties with the Tokugawa shogunal family. Due to this historical background, the Aizu domain wielded substantial influence within shogunate politics throughout the Edo period, ruling an extensive domain compared to other domains, and highly esteemed for both its military prowess and intellectual achievements. Given these deep historical ties to the Tokugawa family, Aizu’s unwavering loyalty to the Tokugawa shogunate far surpassed other domains, and its samurai consistently held the belief of absolute fidelity to their lord, the shogunal family, under any circumstances.

Ingrained adherence to this singular principle within the Matsudaira family inevitably created an unavoidable conflict with the new government forces. Indeed, Katamori Matsudaira, who became domain lord during the late Edo period, strictly upheld this longstanding family ethos and, at the young age of 28, was appointed by the shogunate as the Kyoto Protector (京都守護職), a crucial role responsible for maintaining security in Kyoto. At that time, Kyoto was extremely unstable and violent, plagued by ronin (浪人, masterless samurai) associated with the anti-shogunate factions, particularly those from the Satsuma and Choshu domains, who hid in secrecy and continuously committed acts of aggression. Moreover, numerous reactionary groups opposing these forces also existed, resulting in daily occurrences of violence and murder. Entrusted with this critical responsibility, Katamori Matsudaira entered Kyoto at the end of 1862, leading over a thousand Aizu samurai. The lingering resentment from these turbulent times in Kyoto later became the primary justification for the new government forces—eventual victors in the civil war—to regard the Aizu domain as their greatest adversary.

Consequently, the new government army unilaterally declared war with the goal of completely annihilating Aizu. Additionally, Shuzo Sera, a staff officer under the Supreme Command Headquarters (大総督府), took aggressive and arbitrary measures in various regions, causing widespread confusion among allied domains and leading to an expansion of the war front. Increasing their military strength and advancing northward, the new government army defeated the former shogunate forces in Echigo during the Battle of Hokuetsu (北越戦争). They subsequently emerged victorious in battles at Shirakawa Castle (present-day Shirakawa City, Fukushima Prefecture) and Nihonmatsu Castle (present-day Nihonmatsu City, Fukushima Prefecture), thereby encircling the Aizu domain. This pincer movement ignited the Battle of Aizu (会津戦争) within Aizu territory. However, Aizu-Wakamatsu Castle, renowned for its formidable defensive structure, housed approximately 5,000 soldiers within its walls. As a result, despite possessing modern weaponry, the new government army struggled to seize it, leading to fierce fighting that lasted over a month.

Employing the latest firearms and artillery, the new government forces laid siege to the castle. On September 14, 1868, they launched a massive general assault. Concurrently, the capitulation of multiple domains fighting alongside Aizu, notably the Yonezawa domain, occurred, leading to dire shortages of supplies and leaving those inside the castle in desperate conditions. Eventually, Aizu surrendered on September 22. Thus, the Battle of Aizu concluded, marking the suppression of resistance from former shogunate forces. This tragic event resulted in approximately 2,400 deaths among Aizu soldiers alone, with thousands of civilian casualties as well.

However, even after surrender, the new government showed no mercy. Harsh punishments were imposed upon the defeated Aizu domain, aiming at its total destruction. Katamori Matsudaira, the domain lord, avoided seppuku but faced prolonged house arrest, and all domain territories were confiscated. The domain itself was abolished entirely, and all its samurai were subjected to rigorous surveillance under the new government.

Although this effectively destroyed the foundations of the Aizu domain, in December 1869, the Meiji government allowed the Matsudaira family name to continue in an effort to suppress rebellious sentiments among former Aizu samurai. However, behind this seemingly lenient action lay cunning intentions. The government simultaneously granted a new territory to the Matsudaira family in the remote Shimokita Peninsula in Aomori Prefecture, an area targeted for colonization. Far from being favorable treatment, this policy deliberately isolated the potentially rebellious group in a distant region, ruthlessly exploiting them as colonizers to drain their strength. As a result, most Aizu samurai were forcibly removed from their homeland and resettled in the isolated Shimokita Peninsula.

Moreover, unlike the fertile Tsugaru Peninsula to the west, the Shimokita Peninsula at the northeastern edge of Aomori historically has been unsuitable for agriculture, with harsh winter conditions making colonization efforts extraordinarily challenging. In effect, this amounted to a brutal death sentence for the people of the Aizu domain, already vilified by the new government. It is said that approximately 17,000 former Aizu samurai and their families were relocated to this area, where many suffered from severe hunger and extreme cold. Furthermore, the colonization, primarily led by warriors without agricultural experience, ended in total failure.

In fact, I have personally visited the Shimokita Peninsula multiple times, and to this day, vivid remnants of this tragic history persist. While some towns exist, much of the peninsula remains barren, unable to support agriculture—clearly illustrating that this forced relocation was essentially exile.

Following this, the Meiji government continued to impose relentless pressure on the former Aizu domain and other forces that had opposed them during the Boshin War. An especially crucial perspective emerged later in 1877, when tensions between the samurai of Choshu and Satsuma domains—former allies who temporarily united during the Meiji Restoration—boiled over, sparking a large-scale civil war known as the Satsuma Rebellion (西南戦争). Victory in this conflict ultimately went to the Choshu faction, causing Satsuma’s influence within the government to wane significantly and paving the way for an era dominated by the Choshu faction. Consequently, a skewed power balance emerged in Tokyo (formerly Edo) between northeastern Honshu (the region around Aizu and the former shogunate) and the western Yamaguchi region (former Choshu territory). In reality, this distorted balance of power established during the Meiji era continues to exert influence across many aspects of Japanese society to this very day.