  Though less popular than it once was, international relations was once dominated by realists who argued that political states are not constrained by morality in their dealings with foreign states and individuals. The basic idea motivating this approach was most often the Hobbesian presumption that morality consists solely of contracts which are binding only in the presence of a sovereign who could enforce them. And since there is no world sovereign capable of punishing states, the latter cannot be morally bound by any putative contracts which purport to apply to them. As a consequence, realists have traditionally supposed that states will and should orient their dealings with foreigners in whatever fashion maximally suits their national interests. And if this is correct, there can be no duties of any kind owed to foreign states or individuals, and thus no duty to open one’s borders to foreigners.