Ours is an era marked by extraordinary human migrations, with some 200 million people alive today having moved from their country of origin. The political reaction in Europe and the United States has been to raise the drawbridge: immigrant workers are needed, but no longer welcome. So migrants die in trucks or drown en route; they are murdered in smuggling operations or ruthlessly exploited in illegal businesses that make it impossible for the abused to seek police help. More than 15,000 people have died in the last twenty years trying to circumvent European entry restrictions.

In this...