Yoshimoto invaded Mikawa Province later to subordinate the weakening Matsudaira clan and carried out a westing policy successfully, he fought against the Oda clan in Owari Province who was eager to gain Mikawa in the 'Anjo War,' the 'Battle of Azuki-zaka' and so on, and excluded the Oda clan from Mikawa.
その後は三河国に進出し、弱体化した松平氏を従属させるなど西進政策が次々と実を結ぶ一方、三河に食指を伸ばす尾張国の織田氏と「安城合戦」「小豆坂の戦い」などを戦い、三河から織田氏を締め出した。