Battle of Bonari Pass

What Happened

On 6 October 1868, a defending force of about 800 troops held Bonari Pass (母成峠, Bonari-tōge) against an Imperial army that may have numbered as many as 3,000. The defenders were a mixed coalition: former shogunate soldiers of the Denshūtai (伝習隊, denshū-tai — a Western-style infantry corps trained by French military advisers) and the Shinsengumi (新選組, shinsen-gumi — the shogunate's special police force), together with troops of Aizu and of several northern domains. They were commanded in part by Ōtori Keisuke and Hijikata Toshizō.

The Imperial force was led by Itagaki Taisuke. Moving southwest from Nihonmatsu, Itagaki took a route across Bonari Pass and drove northwards into Aizu. The pass was a strategic access point at the limit of the Aizu fief, and the attack came as a rapid strike against the forces defending Aizuwakamatsu Castle.

Outnumbered, the shogunal troops could not hold the position. They retreated north to Sendai, where the fleet of Enomoto Takeaki was waiting to evacuate them to Hokkaidō. The pass fell, and Aizu was left exposed.

Background

The Battle of Bonari Pass belongs to the Boshin War (戊辰戦争, boshin sensō), the civil war of 1868–1869 that ended shogunal rule and established the Meiji government. It fell in the first year of the Meiji era, and it came late in the campaign year: the fighting had begun in 1868 and had already moved through a series of engagements in the north.

The battle followed the Battle of Nihonmatsu and formed part of the larger Battle of Aizu. Aizu was a domain loyal to the old shogunate, and its castle at Wakamatsu was the objective of the Imperial advance. Bonari Pass was the gateway to that domain — the point at which the road crossed from the territory of the northern domains into Aizu itself.

The defending force reflected the patchwork character of the shogunal side by this stage of the war. The Denshūtai and the Shinsengumi were survivors of the shogunate's own military apparatus, now fighting alongside domain troops from Aizu and other northern domains that had chosen to resist the Imperial government. Ōtori Keisuke and Hijikata Toshizō were among the most experienced commanders remaining to that side.

Why It Mattered

The defeat at Bonari Pass opened Aizu to the Imperial army. With the pass lost, the shogunal troops fell back north to Sendai, where Enomoto Takeaki's fleet stood ready to carry them to Hokkaidō. That evacuation removed the surviving shogunate forces from the main theatre of the war on Honshu.

Aizu itself was left exposed. Three days after the battle, the Imperial troops reached the castle of Wakamatsu and laid siege to it. That siege, the Siege of Aizu Castle, became the key action of the Battle of Aizu.

The battle also marked a stage in the career of Hijikata Toshizō, the Shinsengumi commander, who would continue the fight in Hokkaidō after the retreat. For the Imperial side, Itagaki Taisuke's rapid strike across the pass demonstrated how quickly the government's larger forces could convert a numerical advantage into territorial gain.

The Name in Japanese

The Japanese name is 母成峠の戦い, read ぼなりとうげのたたかい (Bonari-tōge no tatakai). In romaji the name is Bonari-tōge no tatakai.

Broken down character by character:

• 母 — read here as bo. The character means "mother". In this place name it carries no everyday meaning; it is part of the name Bonari.
• 成 — read here as nari. The character means "to become", "to accomplish", or "to complete". Again, in this name it functions purely as a sound element.
• 峠 — read here as tōge (in the compound, tōge; the standalone reading is tōge). The character means "mountain pass" or "ridge crossing". This is the element that tells the reader what kind of place Bonari is: a pass over a mountain.
• の — read no. This is the possessive particle, linking "Bonari Pass" to what follows. It works like the English "of" or the apostrophe-s.
• 戦 — read here as tatakai. The character means "war", "battle", or "fight". Used alone as a noun it is normally read ikusa or sensō in compounds; here, in the form 戦い, it is read tatakai and means "battle".
• い — read i. This is the okurigana, the trailing kana that completes the verb-derived noun 戦い (tatakai). It has no meaning of its own; it fixes the reading of the preceding character.

So the whole name means, plainly, "the Battle of Bonari Pass". The structure is typical of Japanese battle names: a place name, the particle の, and 戦い, "battle".

Key Figures

Itagaki Taisuke led the Imperial troops at Bonari Pass. His force, by some estimates as many as 3,000, advanced southwest from Nihonmatsu and then crossed the pass northwards into Aizu.

Ōtori Keisuke commanded part of the defending force, which included former shogunate soldiers of the Denshūtai.

Hijikata Toshizō commanded Shinsengumi troops in the same defending force. After the defeat, the shogunal survivors retreated to Sendai.

Enomoto Takeaki commanded the fleet at Sendai that was ready to evacuate the retreating shogunal troops to Hokkaidō.