Complex sentence: William resisted him with determination and effectiveness, occupying the fortresses of Acqui Terme, Tortona, and Novi Ligure, and affirming his hold on Nizza Monferrato.
Split into simpler sentences: William resisted him with determination and effectiveness. William even occupied the fortresses of Acqui Terme, Tortona, and Novi Ligure, stabilising his hold on Nizza Monferrato.