benelux

Since 1944, the governments in exile of the Kingdom of the Belgium and the Netherlands and the Grand Duchy of Luxembourg had agreed to a customs union until superseded on this day in 1958 when the three nations ratified the Treaty of Brussels that integrated further the signatories both economically and politically.
This bolstering of cooperation and transparency ran parallel to the European Communities (all of whom were also founding members—the so called Inner Six along with West Germany, France and Italy) created by the Treaty of Paris of 1952 that established the pooling of industrial resources and would eventually serve as the model for the successor European Union. The tight group considered opening membership in 1960 to the Outer Seven—Austria, Denmark, Norway, Portugal (Spain still under dictatorship) Sweden, Switzerland and the United Kingdom—the latter being particularly keen on joining as the Suez Crisis of 1956 (see previously here, here and here) with its intervention efforts undercut by the USA had shown Britain that it was no longer all-powerful and could not thrive without allies. Fearing that UK membership would become a Trojan Horse for American interests, France vetoed Britain joining for seven years until Georges Pompidou succeeded Charles de Gaulle as French president—with reassurances—accepted their application and began negotiations, the community finally expanding in 1972.