If the European Union were simply a club of nations, a forum through which neighboring states could arbitrate their disputes, no one would have a problem with it. And Britain wouldn’t be holding a referendum on June 23 on whether to leave.

What makes the EU different from every international association is that it legislates for its member states. Its foundational treaty, the Treaty of Rome, doesn’t simply bind its signatories as states; it creates a new legal order, with precedence over the national laws of the member nations, directly binding upon individuals.