Hmmm. Western Europe had Protestants and Catholics, and the US had Protestants and Catholics. I failed to notice any great need to paper over religious differences in Europe with transnational structures. That was done to for economic and defense reasons.
PS. And the short, snippy answer to your statement would've been: because in 1945 "Western Europe" did not exist, whereas the United States did.
PPS. And in my post #657 wherever I say Europe I am referring to Western Europe, and specifically its endeavors in opposition to Eastern Europe.
One might say that each society is a mosaic of pieces uniquely arranged to achieve the same final landscape: prosperity. To the extent that the arrangement doesn't produce that outcome, then the pieces are eventually rearranged. Some become obsolete; others may be discovered. Many are interchangeable.
At least that's how I see it!
One additional thing I should note is that I actually haven't given that much thought to the contrast in religious intensity between the United States and Europe. It's a topic that's crossed my mind once in a while but not one I've seriously pondered. Generally what interests me are the grand patterns of history, not the trivial permutations. As I see it, in the grand scheme of things it's of no great consequence if the United States in this regard arrives at the same juncture a few decades later than does Europe. What is of consequence is that they both appear to be headed toward the same destination.
Anyhow, what I'm getting at is that I have no great stake in my above conjecture about the distinction between America and Europe. I could very well be wrong (in my primary attribution of it to geopolitics). That's what strikes me as most plausible, but I am quite open to alternative explanations. The statement that "the well springs of American religiosity run much deeper than that" doesn't help much, because it seems to me the whole sub-question we're examining is: Why? It's not as if the well springs of European religiosity were exactly barren not so long ago..
Finally, look at the ruins of Yugoslavia. Even after 45 years of secular harmony they didn't have any problem finding religious intensity once it again suited their political aims. Ireland is another example: is their political conflict due to religious intensity, or is their religious intensity due to the political conflict? I would submit far more so the latter (and this extends back to their oppression by the English).