In 1957, France, West Germany, Belgium, Italy, Luxembourg and the Netherlands signed the Treaty of Paris, which established the European Economic Community (EEC), the predecessor of today’s European Union. It was the latest of several attempts to foster economic cooperation between European nations in the wake of World War II. Nations that traded together, it was believed, would be less likely to go to war with each other. 

When the United Kingdom first applied for membership in the EEC in 1963, France’s President Charles de Gaulle vetoed its application, reportedly because he didn’t want English to replace French as the dominant language of the Community. The UK finally made it into the club in 1973, but just two years later was on the verge of backing out again. 

In 1975, the nation held a referendum on the question: “Do you think the UK should stay in the European Community (Common Market)?” The 67 percent “Yes” vote included most of the UK’s 68 administrative counties, regions and Northern Ireland, while only Shetland and Western Isles voted “No.” The center-left Labour Party split over the issue, with the pro-Europe wing splitting from the rest of the party to form the Social Democratic Party (SDP).