Border control, territorial rights and feasibility

States more or less universally claim discretionary rights to decide who may or may not cross their boundaries, and to use force and violence to ensure compliance with these decisions. The justification of these practices has received much attention, but I think there is an important underexplored element of this debate. I argue that, in order to provide a plausible justification, it is indispensable to ask questions about feasibility. Any plausible defence of anything like the kind of border control regime actually in force will need to pay close attention to social scientific research into feasible alternatives.