<論説>薩長同盟の展開 : 六ヶ条盟約の成立

Abstract

慶応二年一月に薩長が結んだ六ヶ条の盟約は通常「薩長同盟」と呼ばれ、武力倒幕を目指す政治・軍事的提携の「成立」とみられてきた。だが同盟は、既に慶応元年九月に成立していた。本稿では六ヶ条盟約を同盟関係の「展開」の一段階と位置づけ、その成立過程を以下のように論証した。同年九月に長州再征勅許が出されたのをうけ、薩摩は再征阻止に向け軍事力行使を決意した。しかし幕府は進軍せず情勢不透明となり、戦略を相談し直すべく、慶応二年一月に木戸孝允・西郷隆盛らの京都会談が実現した。会談で西郷は、事実上の再征撤回を含んだ幕府側の処罰令受諾を勧めたが、木戸は処罰を頑なに拒否した。藩主の方針に矛盾し、他藩も納得し難いこの強引な村応は、木戸が社稷存続を第一義におく藩官僚から、藩を道具としてでも国家的構想に立つ政治家へと脱皮していたためであった。この平行線の状況下に坂本龍馬が到着、その周旋により西郷らは譲歩し、盟約は成立する。六ヶ条盟約とは、薩摩が長州の処罰一切拒否論を承認し、その結果可能性が高まる幕長戦争についても全徳川勢力との決戦を約束する、というものであった。つまり薩長の政治的提携関係は、成立当初より一貫して軍事同盟という性格を帯びていたのである。

The six-article pledge which Choshu contracted with Satsuma in the first month of the second year of the Keio era (1866) is usually called the "Satsuma-Choshu Alliance." It has been regarded as the starting point of the political and military tie-up that aimed to "overthrow the bakufu" 倒幕. However, the alliance had already been concluded in the first year of Keio (1865). Therefore, the six-article pledge was only one step in the development of the alliance. In September of 1865, a second punitive expedition against Choshu was given imperial sanction. Satsuma opted to buildup its military strength in order to prevent it. However, the bakufu 幕府 did not attack. The situation was opaque and Kido Takayoshi and Saigo Takamori and others met in Kyoto in the first month of the next year to consult about revising their strategy. Since it appeared to include a halt to military operations, Saigo recommended acceptance of a punitive order from the bakufu. But, Kido stubbornly refused to do so. This forceful response was contradictory to the policy of the lord of the domain, the hanshu 藩主, and was not acceptable to other domains, han 藩, either. It was due to the fact that Kido had transformed himself from a local bureaucrat concerned primarily with his own domain into a politician who stood for a nation in which the domains might play the part of mere pawns. In the end, the pledge was concluded through the good offices of Sakamoto Ryoma. As a part of the pledge, Satsuma recognized the Choshu's stance of total rejection and vowed to participate in the decisive battle against all Tokugawa military forces if, as it appeared increasingly likely, war was to begin over the refusal of Choshu. The political alliance between Satsuma and Choshu was thus imbued with a military character from the time of its formation.