In the end, the history of the United States, like the history of any nation, is a mixed bag. There are moments that inspire us to express the deepest forms of patriotism and love of country. There are moments as well that cause us to hang our collective heads in shame.
So what are Christians to do? How do we live as members of the Kingdom of God and citizens of this great and flawed nation? I think the answer is simple: work for the Kingdom of God regardless of whether we live in a Christian nation or have ever lived in a Christian nation. The first-century church understood this. They sacrificed their lives to advance the Kingdom of God in a Roman empire that was, at least for the first several 100 years, anything but a Christian empire.
So let's be proud of our American heritage but, more importantly, let's be diligent in remembering that our highest calling as Christians is to be faithful members of the Kingdom of God. As Jesus put it, "Rejoice and be glad, for your reward is great in heaven."