Short Abstract

The assassination in 1219 of the third shogun, Sanetomo, remains both mysterious and significant. This paper unpacks the motives behind the powerful political figures who manipulated the assassin while highlighting how Sanetomo’s demise triggered events that changed the course of Japanese history.

Long Abstract

The creation of the Kamakura shogunate—Japan’s first samurai government—is widely recognized as a watershed moment in Japanese history. Founded by Minamoto no Yoritomo in the 1180s, it seems to mark the start of something enduruing: almost seven centuries of warrior rule. But far less attention is paid to the demise of Yoritomo’s line just a few decades later. This paper sheds new light on one of the darkest moments of Kamakura history: the assassination of the third shogun, Minamoto no Sanetomo. It is also a case study in the ways that leading thirteenth-century figures used ideas of “revenge” and “honor” to advance their own political agendas.

Late in the first month of 1219, Sanetomo was murdered by his own nephew on the grounds of the Tsurugaoka Hachimangu Shrine. The nephew believed that he was exacting revenge for the death of his own father some fifteen years earlier, but his actions had much more profound consequences for Japan’s first warrior government. Sanetomo’s assassination not only brought an end to the direct line of Minamoto shoguns but also created a leadership crisis that led to the first (and only) female shogun, the securing of power by the Hojo regents, and the outbreak of war between the imperial court and the bakufu in 1221.

The paper draws on a wide range of primary and secondary sources to argue that Sanetomo’s murder was far more complex than a simple case of revenge; instead, it contends that the nephew was manipulated by relatives and other political figures eager for a shift in the balance of power. By reassessing the motivations and machinations of key bakufu figures, the paper highlights the fragility of the early warrior government as it searched for new solutions to ongoing problems of succession and legitimacy. It also looks at the broader role that concepts of revenge and assassination played in early medieval warrior society.