The Shinano Mountains matter less as a described landscape than as a point of political and military control. Toranaga’s plan depends on securing passage through them: whoever controls this route can shape the movement of armies toward the Osaka plains and the Kwanto.

A Corridor in Toranaga’s Alliance Bargain

Toranaga offers Saigawa Zataki a secret alliance, a joint attack on Ishido under Toranaga’s command, and the lands of Christian daimyos who oppose him. In return, he asks for guaranteed safe passage for his armies through the Shinano Mountains. The bargain’s family terms underline its stakes: as a measure of trust, Toranaga offers to send his son Sudara, Sudara’s wife, and their children, including Toranaga’s only grandson, to Zataki at Takato.

Toranaga recognizes that the offer is a strategic trap as well as an appeal. The mountains lie across his only road, and Zataki’s cooperation could open the approach to the Osaka plains. The alliance therefore hinges on more than shared opposition to Ishido: it requires Toranaga to secure movement through a route whose access is in another lord’s hands.

A Northern Defensive Position

Toranaga’s wider war plan gives the northern approach a distinct role. After the rains, he expects Ishido to attack the Kwanto in a simultaneous pincer: Ikawa Jikkyu would lead from the south, while Zataki would press from the north. Toranaga plans to contain Jikkyu at Mishima, then withdraw toward the Hakoné Pass and Odawara for a final stand. In the north, his forces would hold Zataki in the mountains along the Hosho-kaidō Road, somewhere near Mikawa.

This plan presents mountain terrain as a means to delay and contain an advancing force. Toranaga’s strategy is not to meet the full invasion at once; he intends to fight, fall back, and wait until his allies and circumstances make a decisive attack possible.

Strategic Significance

The Shinano Mountains link geography to negotiation and military timing. Safe passage through them is a condition of Toranaga’s proposed alliance, while the northern mountain position figures in his plan to slow Zataki’s advance. In both contexts, the mountains constrain movement—and make control of movement a source of power.