Complex sentence: In 1794, on the departure of Westmorland, his successor as Lord Lieutenant, (possibly, William Fitzwilliam, 4th Earl Fitzwilliam) halted construction, eventually Vallancey was allowed to continue but the Fort was still incomplete in 1797.
Split into simpler sentences: In 1794, on the departure of Westmoreland, his successor as Lord Lieutenant, (likely William Fitzwilliam, 4th Earl Fitzwilliam) halted construction. Eventually Vallancey was allowed to continue but the fort was still incomplete in 1797.