Battle of the Kanna River

The Battle of the Kanna River, fought from the 16th to the 19th day of the sixth month of Tenshō 10 (July 5–8, 1582) around the Kanna River in Kami district of Musashi Province, is remembered as one of the largest field battles ever fought in the Kantō region during the Sengoku period. The political vacuum created by Oda Nobunaga's death at Honnō-ji spilled directly into a massive engagement that reshaped the balance of power in eastern Japan.

Following the fall of the Takeda clan in the Kōshū campaign, Nobunaga had rewarded his senior retainer Takigawa Kazumasu with Kōzuke Province and two districts of Shinano in March 1582, entrusting him with governance of the Kantō frontier and incorporating the former Takeda "Jōshū" retainers into his command. But when Nobunaga was killed by Akechi Mitsuhide on the second day of the sixth month, the Hōjō of Odawara seized the chance to sweep the Oda presence from the Kantō. Hōjō Ujinao and Ujikuni marched north with a great army.

In the opening clash on the 18th, Kazumasu's forces stormed and took the Hōjō-held castles of Kanakubo and Kawai and won the fight on Kanakubo Plain, inflicting heavy losses. But when Hōjō Ujinao arrived with the main body on the 19th, the tide turned. Facing roughly 56,000 Hōjō against his own 18,000, and with the Jōshū lords deserting after days of fighting, Kazumasu was driven back to Karasu­gawa Castle. The battle was fought largely as close-quarters combat with sword and spear; by the late Sengoku period the uchigatana had become the standard combat blade in the Kantō, sustaining demand from regional smiths. Kazumasu conducted an orderly retreat over the Usui Pass through Komoro and the Kiso road, reaching Nagashima Castle in Ise by the first of the seventh month. The Oda presence in the Kantō was destroyed, feeding into the ensuing Tenshō-Jingo conflict over the former Takeda lands.