Complex sentence: Many of the castles within Morgannwg were attacked by the forces lead by Owain Glyndŵr during the Welsh Revolt of 1400-1415, some were captured and several were damaged to such an extent they were never maintained as defences again.
Split into simpler sentences: Many of the castles within Morgannwg were attacked by forces led by Owain Glyndŵr during the Welsh Revolt of 1400-1415. Some were captured, and several were damaged to such an extent they were never maintained as defences again.