interesting topic
but, I think Japan is off topic for comparison since it's not even a Christian nation.
as far as comparing the US to Europe...the bible says that godlessness will spread in the last days. not sure if it matters that some areas of the Christian world are farther along in that process than others. though perhaps the US is Mystery Babylon and will play a role in defending Israel in the run-up to the antiChrist being revealed.
The US isn't a Christian nation either, John Adams says so.
Because we are younger than Western Europe/Japan.
Wouldn't that have the opposite effect?
No, we have a younger history than Western Europe/Japan, and when they were younger they were more religious but the "grew out" of it. Canada managed to "grow out" earlier for some strange reason/