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The United States has become a caricature of itself. Like when the assistant secretary of state for Europe, Philip Gordon, traveled to London to lecture the British government on why it should remain in the European Union.

Throughout its existence Britain has enjoyed an identity separate from Europe. The British Isles were only a late and distant addition to the Roman Empire. The next invasion wasn’t until 1066. Since then none has succeeded: Britain fended off Spain’s King Phillip II, France’s Emperor Napoleon and Germany’s Adolf Hitler.

The UK kept its distance from the continent, switching allies like they were dance partners at a costume ball. After World War II, the European Union began as a more rudimentary continental Common Market...