In 1952, a bunch of European nations decided they were sick of going to war with each other a few times every century. To foster non-zero-sum relationships and co-operative economic growth, the Western European powers formed a common market for the coal and steel trades, which they named, somewhat uncreatively, the European Coal and Steel Community. In 1967, this evolved into a broader free-trade zone called the European Economic Community, which the U.K. joined in 1973. By the early 2000s, these European nations had taken their relationship to the next level — establishing a system of open borders, uniform regulations, a complicated political and economic bureaucracy based in Brussels, and a common currency, the “euro.”
But even then, Britain wasn’t comfortable with that kind of commitment. It retained its own currency (the pound) and didn’t fully dismantle its border controls.
