ROGER WALDINGER: The massive and still accelerating cross-border movement of people across the globe might be the most portentous development of our times.

Put in historical perspective, it is safe to say that more people, and people from a greater variety of nations, are crossing national borders today than at any time since the modern state system came into being, and that still more would do so if they could. The cumulative implications for global economy and comity are as enormous as they are generally underappreciated.

In restricting migration, governments of course do what their people want. Public opposition to open borders is near-universal; majorities want tougher, not looser, controls on the border in virtually all economically advanced countries, and even in many that are not as wealthy.

Politicians, however, are generally dissatisfied with the voters they have, and inclined to import those who might be more pliable.