Or was it collaboration in defense of their self-interest? After WWII Europe was in ruin, the USA and USSR had taken over as the world powers, and the sentiment

Or was it collaboration in defense of their self-interest? After WWII Europe was in ruin, the USA and USSR had taken over as the world powers, and the sentiment "never again" clearly had not proven to strong enough in the past. Making the same mistakes as after WWI was not an option this time. Furthermore, Western Europe found in the USSR a common and real enemy. As Germany was divided into four (later two) parts, the power balance between France and Germany favored France at that time. That allowed for the idea of a collaboration that would connect the re-development of Germany to the development of Western-Europe as a whole. As a result, so hoped the Europeanists, France and Germany would become co-dependent to that extent that a military solution would not be in the interest of either country. To keep that balance, however, neither country could afford to annex some of the smaller countries. That would make the European idea attractive to these smaller countries. All idealism aside, all this can be explained from a Realpolitiker point of view. PS It has been a while I since studied International Relations and Modern History, however, so take the above more as informed speculation than historical analysis.