The United States is not a Christian nation. The two most powerful countries other than the US are not Christian nations. There won't be a Christian nation until Christ sets up His kingdom.
Right, it's not a theocracy.
Nonetheless, it was founded on Judeo/Christian beliefs and the concept of individual freedom first came to the USA, then eventually Western Europe.
Regardless of what you believe, we today have never had it better and things could be far worse.
All you have to do is look around the world and see how bad things could be had you been born there instead of here.
What we have didn't just happen. The founding fathers, especially the signers of the Declaration of Independence like Jefferson and Adams, didn't have to. They were already wealthy aristocrats who
were politically in bed with the British. They could've just gone back home and lived their lives. Instead, they believed in something and wrote it down in the Declaration of Independence. As soon as they signed the document, they were wanted for treason and if caught would've been hung.
Sure, the nation wasn't perfect, but it evolved and hopefully is still evolving for the good.
Unfortunately from what I see, we're devolving and will lose the liberty we have. How long that will take and what the process will be, I'm not sure. I probably won't be alive to see it, or too old to do anything about it anyway.