Re-read what I said. We are a "Christian nation" insomuch as the majority of our populace is Christian. Germany is a "Lutheran nation," England an "Anglican nation," Pakistan a "Muslim nation," China a "Buddhist nation," and so on and so on. We are not a LEGALLY Christian nation, as the Christian religion is not codified in law. We are a SOCIALLY Christian nation, as the majority of our population is Christian.
We are different from all the other nations you mentioned in that we are not an indigenous race ethnicity or nationality. The comparisons don't work.