The expansion was mainly a consequence of tactics of Katsumoto to Western camp daimyos (including the Ouchi and Toki families) to harass the rear, and the expansion included substantially the whole country except the provinces of Ou, Kanto, Echigo, and Kai.
これは勝元による西軍諸大名（大内氏・土岐氏など）に対する後方撹乱策が主な原因であり、その範囲は奥羽・関東・越後・甲斐を除くほぼ全国に広がっていった。