反乱軍は山岳地帯を根拠として抵抗を続けた。
The rebel army kept up its resistance, using the mountains as its base.
海賊たちはこの島を根拠に周辺の海を荒らし回った。
The pirates used this island as their base to raid the surrounding seas.
一族は京都を根拠に全国へ勢力を広げた。
From their stronghold in Kyoto, the clan extended its power across the country.