Complex sentence: Under its new name of Fort Cumberland, the Beauséjour Ridge fort became a strategically important British military emplacement as it guarded the overland route to peninsular Nova Scotia and also the upper reaches of the Bay of Fundy.
Split into simpler sentences: Under its new name of Fort Cumberland, the Beauséjour Ridge facility became a strategically important British facility. It guarded the overland route to peninsular Nova Scotia, as well as the upper reaches of the Bay of Fundy.