In the previous post, I said that there is no one particular day when the European Union could be said to have been formed, and that is true. The essence almost of the EU and its formation is in its gradualism. As I said then, the ideas of a peaceful integration of the states of Europe has its origins as early as the First World War or even earlier.
But if you had to choose a day above all others which could act as the European counterpart to the American Declaration of Independence, which set that great nation on its path, then it would have to be May 9th 1950, the day of the so-called Schuman declaration. Many commentators agree that this was an historic day for Europe, and as such, May 9th is celebrated as a holiday (Europe Day) in many places within the borders of the EU.
The reason it is so momentous is that once the Schuman plan was put into effect, a process was begun which would not be easy to reverse, and as the years went by, became increasingly less likely to be reversed. Perhaps at the time, many of the participants in the plan were not aware of how irrevocable it was, but it has now become clear that the European Union as it is now is a direct result of that decision. So the Schuman Declaration, more than anything else, could be said to be the cause of the European Union.
It is true that the council of Europe, for example, had already been in existence since 1948, but it was the agreement to follow the Schuman plan which tied the Six together in an economic agreement. In particular, it meant that, ever after, France and Germany had no choice but to work in partnership.
On this link, you can watch the ceremony of the unveiling of a sculpture of Robert Schuman at the University of Cork in Ireland, and some beautiful readings by children from France and Ireland. http://eurofile/2008/12/robert-schuman