sentences:  His participation in Guelph politics and the planned invasion of Lombardy with Charles I of Naples, caused a war with Oberto Pelavicino, the chief Ghibelline commander in the region, in 1264.William resisted him with determination and effectiveness, occupying the fortresses of Acqui Terme, Tortona, and Novi Ligure, and affirming his hold on Nizza Monferrato.In 1265, French reinforcements arrived.