THIS summer, a striking, often tragic story has been playing itself out on the outskirts of Calais in France, at the entrance to the tunnel that connects the European mainland to Great Britain. Thousands of migrants, African and Middle Eastern, have been trying to sneak onto the trucks and trains that traverse the tunnel, cutting through wire fences and evading the police along the way. Ten have died, but enough have succeeded for many more to keep trying, while politicians on both sides of the Channel point fingers and a refugee camp outside Calais remains swollen with would-be subjects of Elizabeth II.

In certain ways this crisis resembles last summer’s border surge in the United States, when a wave of juvenile migrants overwhelmed the border patrol’s ability to cope. But mostly Calais highlights two major differences between the immigration issue in America and Europe, two ways in which migration — from Africa, above all — is poised to divide and reshape the European continent in ways that go far beyond anything the United States is likely to experience.

The first difference is illustrated by the Calais migrants’ desire to reach not only the European Union at large but the specific destination of Britain — because of its relatively stronger economy, because they speak English, because the U.K. doesn’t have a national identity card, or for other reasons still.

An immigrant desire to go further up and further in is entirely normal. (Mexican immigrants to the United States do not all settle down in El Paso or Tucson.) But it poses a major dilemma for the European Union, which allows free movement across its internal borders, but which is composed of nation-states that still want sovereignty over their respective immigration policies.