An interesting question has been posted by Jane Galt
Is Europe's peace and unification a result of a philosophical evolution, or the fact that we have essentially made Europe an occupied protectorate of the United States for the last 50 years?
I think American military presence in Europe affected European philosophical evolution.
With the exception of the western portion of Germany under the control of the western Allies (US, UK, France) American occupation of Europe was not designed to, nor did it, militarily threaten any western European nation. After the formation of NATO in the face of the threat of Soviet expansionism, even West Germany was no longer threatened by the occupation. To me, that means that, even though the US troops stayed put, the "occupation" ended, at the latest, with the formation of NATO. It simply wasn't an occupation any more. West Germany was our ally in both name and deed. The presence of the US Army in West Germany was no more an occupation of West Germany than the presence of the US Army at Fort Leavenworth was an occupation of Kansas. The presence of US military forces in Europe was no longer aimed at keeping a resurgent Germany from rearming and threatening its neighbors, or keeping the peace among western European nations. The purpose was to deter (and, failing that, to oppose) a Soviet invasion.
Our post war presence on German soil, both initially as occupying conquerors and later as invited allies had the effect of allowing a economically and militarily exhausted western Europe to forego the cost of preparing to fight a third European war, and, to a large degree, similarly avoid the cost of defending Europe against the Soviets. The inevitable result was that West Germany was seen to have been neutralized as a military threat to Britain and France, and all of western Europe therefore ramped up spending on a socialist or quasi socialist political and economic agenda and allowed their respective militaries to deteriorate.
My father once observed that when a practical man fails at something, he tries a different solution to the problem, but that when a idealist fails, he often attempts to impose the same failed solution on more people. The problem with gun control, for example, was not that controlling guns in, say, New York was impossible or impractical, it failed only because other states refused to go along and prohibit the sale of guns to New Yorkers. The idealist's solution is not to try something else in New York, it is to impose the policy which had failed in New York on a larger group of people. The same mindset gives rise, in part, to the present war on drugs. Because the government has utterly failed to control domestic consumption of illegal drugs, it is attempting to impose its anti-drug policy on those foreign nations which are home to the producers of drugs illegal in the US.
I think the same dynamic is at work in Europe, today. The individual members of the EEC could not successfully apply many of their overly idealistic policies within their own borders. Each national economy subject to those policies became less and less efficient and experienced higher and higher unemployment, and each sovereign nation had a strong incentive to make its policies just a little less restrictive than its neighbors. The result in the US would normally be the widespread adoption of minimalist restrictions. Not so in Europe. Unification is an attempt to apply those same failed policies on a continent-wide basis. I think that most of the policies failed not because the policies of a neighboring nation were slightly different, but because the policies themselves are economically unworkable. Changing the number of people or nations to which those policies appy will not change the economic viability of the policies. It will only change the number of the people burdened by them. For example, the drive for equalization of the tax structures of the member nations has become, in fact, a drive to tax all people at the highest rate of any individual member nation, otherwise the citizens of low tax members like Ireland have an "unfair advantage." The low tax regime in Ireland does in fact give it and its citizens an economic advantage over much of the rest of Europe, and it did so before unification. Unification allows those with the self imposed disadvantage to level the playing field by imposing a similar disadvantage on the others.
On an oversimplified basis, the urge to control "just a little bit more" to achieve the desired result is in large part what drives European unification. That desire for control arises from the socialist mindset now widespread in Europe. The socialist mindset is, ironically, enabled by the post war American military presence in Europe.