I'm sorry but that's not the case, I wish it were. Maybe in terms of numbers Christianity has had the majority; but officially the US isn't a "Christian nation." It's a nation of any and all religions that promote peace and liberty. That's not me saying that but the Constitution.
The US was founded on "Biblical principles," but Biblical principles alone don't make anything Christian. Islam, Buddhism or any other religion can follow moral principles found in the Bible, that does make them Christian. There's nothing in official US policy or in the Constitution that states: "These USA are a Christian nation." That was the intention of many of the founders, but it's not the way it worked out.
The US was founded on "Biblical principles," but Biblical principles alone don't make anything Christian. Islam, Buddhism or any other religion can follow moral principles found in the Bible, that does make them Christian. There's nothing in official US policy or in the Constitution that states: "These USA are a Christian nation." That was the intention of many of the founders, but it's not the way it worked out.