Complex sentence: By the end of the 16th century the Grants were a powerful force in the Highlands, though Urquhart itself saw little further action until it was captured by a Covenanter force in 1644.
Split into simpler sentences: By the end of the 16th century the Grants were a powerful force in the Highlands, though Urquhart itself saw little further action. Urquhart was captured by a Covenanter force in 1644.