What you write may be true but all I can say is that luckily for us the "black robed brigade" from the Revolutionary War days felt much different about the church's and their role in the political matters of the day. It's pretty obvious that one of the major driving forces in organizing the citizenry to stand up and fight the British were the pastors and various church leaders who were instrumental in organizing and motivating the colonists. I guess their interpretation of the New Testament was somewhat different than what we're witnessing today.
I think you are right. The early colonists, as well as many ON BOTH SIDES of the Civil War, were christians. In the case of the Civil War, pastors on both sides used their pulpits to drive the war effort; in the North, they cried "free the slaves, God wills it" and in the South, they cried "free your homeland, God wills it".
The reason both sides could enlist christians to kill each other is simply that the New Testament supports neither argument, equally.
Neither Jesus nor Paul had any interest in the concept of dying or killing for a country.
In fact, Jesus explicity rejected that option: "IF MY KINGDOM WERE OF THIS WORLD MY SERVANTS WOULD FIGHT."