In 1560, Yoshimoto IMAGAWA was killed by Nobunaga ODA of Owari and Shingen, whose attempts to invade the north had been thwarted by Kenshin UESUGI of Echigo, revised his plans, abandoning his alliance with the Imagawa clan and planning invasions of Suruga-no-kuni (Suruga Province) and other provinces in the Tokai region.
永禄3年（1560年）、桶狭間の戦いにおいて今川義元が尾張の織田信長に討たれると、信玄は越後の上杉謙信の介入で滞っていた従来の北進政策を改め、今川氏との同盟を破棄して駿河国など東海地方への侵攻を企て始めた。