Complex sentence: There was much unrest in the area during this time because Cheraw fell into part of the British strategic line of defense, where garrisons were built to control revolutionaries and to encourage loyalists.
Split into simpler sentences: There was much unrest in the area during this time because Cheraw fell into part of the British strategic line of defense. This British strategic line of defense was where garrisons were built to control revolutionaries and to encourage loyalists.