Historically, however, governments have often been as concerned with emigration as they have been with immigration.

This is not surprising since government have always attempted to "monopolize the legitimate means of movement" as noted by historian John Torpey. For Torpey, author of The Invention of the Passport: Surveillance, Citizenship and the State, a preferred method of "regulating international movement" has been the passport. Wendy McElroy puts things less subtly when she describes the passport as a tool the state can use to "exert social control by refusing travel to 'enemies of the state.'"

It should not be surprising, then, that the US government is now cracking down on Americans who have outstanding tax bills — by holding their passports hostage. This could affect more than 360,000 Americans.