In Europe, religion has been losing its importance for quite some time. At one time, the catholic church would choose who the rulers of Europe were, and they had a “divine right” to rule. That monarchy has now almost completely disappeared aside from a few symbolic positions. I don’t know the exact reason this has happened but when the nobility no longer requires people to be of the same religion, the importance of religion to the average person will be much lower. Also, the horrors of war in Europe probably led many to question their beliefs. In their minds God is either not all-loving because he lets terrible things happen, or he is not all-powerful and cannot stop bad things from happening.
I would wager that this will probably happen in America, but not to the same extent.