Complex sentence: During the English Civil War, the palace was used as a biscuit factory and prisoner of war camp, then with the Interregnum, the palace and park were seized to become a'mansion' for the Lord Protector.
Split into simpler sentences: During the English Civil War, the palace was used as a biscuit factory and prisoner-of-war camp. Then, in the Interregnum, the palace and park were seized to become a'mansion' for the Lord Protector.