If America, UK or any other piece of real estate was quote, "Christian" - then everybody within would be saved.
Thus just as this world is not, never has been, nor ever will be "Christian" - NO nation is Christian.
God never established this position in any Nation and only HE can make anyone or any group Christian.
9 What then? are we better than they? No, in no wise: for we have before proved both Jews and Gentiles, that they are all under sin; 10 As it is written, There is none righteous, no, not one: 11 There is none that understandeth, there is none that seeketh after God. 12 They are all gone out of the way, they are together become unprofitable; there is none that doeth good, no, not one.