Creation of European coal and steel community in 1951.
Creation of European economic community in 1957.
Maastricht treaty and formal creation of Union in 1992.
Explanation:
After WW2 ended an idea that Europe should be united was wide spread. It is interesting that those who proclaimed it the most were France and Germany. That is why in 1951 ECSC was created with a participation of just a couple of countries, including the Benelux countries. Today EU is one of the biggest unions in the world.
