Complex sentence: The Pontic forces, encamped in the valley, sent out numerous foraging parties which plundered and burned the countryside, Sulla, however, was unable to defend the region with his far smaller force and instead stayed camped on the hill.
Split into simpler sentences: The Pontic forces, encamped in the valley, sent out numerous foraging parties which plundered and burned the countryside. Sulla was unable to defend the region with his far smaller force and instead was forced to stay camped up on the hill.