In 1554, Harunobu formed an alliance with the Gohojo clan and with the Imagawa clan, to make the rear side of his territory safer (an alliance among three provinces of Kai, Sagami and Suruga).
天文23年（1554年）、晴信は後北条氏、今川氏とそれぞれ同盟を結んで背後を固めた（甲相駿三国同盟）。