Christians have a mixed relationship with nationhood.
Some of the first Christians, in the days of the Roman empire, were persecuted by the Roman government. Their leader was accused of seeking to bring in another kingdom. Even though Jesus said his kingdom was “not of this world,” the Romans were skittish about any kind of movement that might threaten their hold on Palestine, where the first Christians appeared. The Jewish people had always been restive under Roman rule.
Eventually, the religion of Jesus conquered the Roman world, not militarily but with its message of love and care for all, even enemies, over selfishness and material gain. Loving your enemies is a terrible weapon against them.
The breakup of central power as tribes from beyond the empire broke through to settled areas brought more challenges. Christians had to wrestle with varying amounts of power and what to do with it.
As Christianity became a majority religion, its leaders began a struggle, still with us, as to how important political power would be to the religion. In Europe, varying groups committed horrendous crimes against each other supposedly for the cause of their particular brand of “Christianity.”
The discovery of new continents gave dissenting religious groups places of refuge. Perhaps the numbers and variety of the dissenters is what led eventually, though not evenly, to our much praised “freedom of religion” in the United States.
Surprisingly, the number of Christian groups in the new country mushroomed for several centuries, despite the absence of a state religion. Could it be that giving freedom to believers for their own religious directions actually made Christianity stronger? Perhaps it freed them from political power struggles.
New challenges of war and the struggles of people in countries formerly governed by absolute rulers led to new ways of thinking. American Christians, having become more numerous as a result of their freedom to believe without government oversight, greatly influenced the country as it grew in both population and in size.
However, the success of religious groups in the United States may have led to a possible loss of influence. As Christianity became, practically speaking, a sort of “state” religion, perhaps its members became more like members of European established churches. Christianity may have lost some of its vitality, just as established European churches did.
At any rate, supposing any country, including the United States, is a “Christian” nation, or ever has been or ever could be, tempts us with a weakened Christianity. We tend to worship America instead of Jesus.
Jesus doesn’t need nationalistic trappings. Indeed, movements which lead in that direction only weaken the Christian message.