If i must choose the first and more important cause for the creation of the European Union surely i would choose the wish of peace between some europeans after the WWII. After long years of cold war, and any wars in european countries we can tell today European Union find no more wars in their current and future territories. That make very unlikely see the European Union giving steps towars any war or conflict.
The economic side of the European Union is very important, and more in time of crisis, but in Europe not all are economic issues. The peace is first and they are more important issues.
The European Union currently have 27 state members with 23 official languages (only Austria, Luxembourg, Cyprus and Belgium don't give a new own language to the union). That let see cultural issues are importants in Europe, and everyone like a good place for their own culture. The European Union laws are very stricts in the defense of the rights of minorities because each people, each culture, have their little minorities in other countries, and all have interest in the defense of minorities. In the European Union your minorities in other countries will be respected, but you must respect the minorities what you have inside.