Every living person is entitled to a nationality, says the Universal Declaration of Human Rights. This right is granted not by a benevolent international body but by individual nations. And every day, governments all around the world wield this power: naturalizing new citizens; denying citizenship to others who apply; and occasionally, revoking the citizenship of a select few. To be stripped of one's citizenship rights is to be consigned to a ghetto of one: the most complete form of exclusion, short of death or solitary confinement. The exclusion of Jews from German society or the denaturalization of more than a million Soviet citizens are obvious examples of this form of social control. But it's not just Nazis, fascists, and dictators from another century who engage in such practices.