Throughout history, border walls and fences have been built for defense, to claim land, to signal power, and to control migration. The costs of fortifications are large while the benefits are questionable. The recent trend of building walls and fences signals a paradox: In spite of the...

Throughout history, border walls and fences have been built for defense, to claim land, to signal power, and to control migration. The costs of fortifications are large while the benefits are questionable. The recent trend of building walls and fences signals a paradox: In spite of the...