Castles, settlers, and the cost of occupation

The Ring of Iron is powerful, but Edward I cannot afford to be strong everywhere. A permanent occupation army large enough to control Wales indefinitely would cost too much. Castles therefore buy time, providing secure points from which royal authority can survive crises. Edward also brings in settlers and establishes settlements around controlled places. The policy rests on the hope that newcomers will intermarry with local people and gradually fuse with the population, following the same pattern credited with changing southern Wales. In this explanation, castle building and settlement offer a way to extend control while limiting the cost of permanent occupation.