The Brussels Treaty of 1948 was a mutual defence pact signed by Belgium, France, Luxembourg the Netherlands and UK. In 1954 The Brussels Treaty was modified and the Western European Union was formed with the addition of Germany and Italy. In addition to the defence pact one objective was to promote the integration of Europe.
The WEU was eventually folded into the EU in 2002 as part of the Common Foreign and Security Policy and the WEU ceased to exist after 2011.
Belgium joined the European Coal and Steel Community in 1951 and European Atomic Energy Community in 1957.
Belgium was one of six original founders of the European Economic Community in 1957 with France, Germany, Italy, Luxembourg and the Netherlands as part of the Rome Treaty.
Brussels contains some major EU institutions including the Commission and one of the European Parliament buildings.
Belgium: joined the single currency on 1 January 1999; and ratified the Lisbon Treaty in 2007 which came into force in 2009.
Belgium is part of the BENELUX Union between Belgium Netherlands and Luxembourg.