Complex sentence: The Belgians later retreated to Turnhout, allowing the Dutch to set up camp, but the sound of Dutch artillery scared the population of Turnhout and people started to flee towards Antwerp "en masse".
Split into simpler sentences: The Belgians later retreated to Turnhout, allowing the Dutch to set up camp. The sound of the Dutch artillery scared the population of Turnhout and people started to flee towards Antwerp "en masse".