In the beginning of the war, forts surrounding Osaka-jo Castle were overrun like what happened in the battle of Kizugawaguchi (1614) and Bakurobuchi, and other forts were abandoned and the troop retreated to Osaka-jo Castle and they were also defeated in the battle of Noda and Fukushima.
緒戦では木津川口の戦い(1614年)、博労淵の戦いなどの大坂城の周辺の砦が攻略され、残りの砦も放棄して大坂城に撤収、野田・福島の戦いでも敗れる。