Complex sentence: Some American historians maintain that the expedition to recapture Mackinac Island was a waste of resources and that the troops would have been better employed in the battles on the Niagara peninsula and the crews of the vessels more use in the squadron on Lake Ontario.
Split into simpler sentences: Some American historians maintain that the expedition to recapture Mackinac Island was a waste of resources. The troops would have been better employed in the battles on the Niagara peninsula and the crews of the vessels more use in the squadron on Lake Ontario.