The book, The Christian Attitude to War, by Loraine Boettner was a fair examination of this topic, even addressing the views of Pacifist Christians and conscientious objectors. "Individuals who desire peace at any price, soon find there are others who are ready to take unfair advantage."
He looks at compulsory military training, blindly obeying government, the Old and New Testament teaching about war, and the idea that military and police forces are based on a similar principle. He also addresses the use of deadly force and the concept that "they do not bear the sword in vain."
Just as no one would advocate abolishing police protection in our cities, or anarchy would result, the use of armed forces is similar, protecting the borders of our country.
He also asserts that the two primary reasons why the U.S. has not been attacked (this was written in 1985), is her favourable geographical location and her recognized ability to defend herself. I would add that the same is true for Canada, except that our ultimate defense comes from our big brother to the south (should they be so inclined), and the aggressors of the world know that.
His thesis is this: "War is justifiable, of course, only when all favourable efforts to avoid it have failed. But when a nation is invaded, its people killed or threatened with slavery worse than death, and property destroyed, it has no alternative but to resist--by any means and at any cost. To fail to resist under such conditions is both immoral and un-Christian. The priceless principles of religious and civil liberty for ourselves and for those who come after us are more important than life itself. Quite plainly, there are some things worse than war."
His explanation of the teachings of Christ are very clear. The idea of turning the other cheek relates to personal injustices and individual attitudes to them. A person has a right to sacrifice himself, but he doesn't have the right to sacrifice others. "I am not to turn my wife's cheek, or the cheek of the weak and defenseless whom I am called upon to protect." He adds that going into the firing line is in very truth turning the other cheek--letting the enemy smite our cheek rather than that of those we love.
Jesus also gave instructions for soldiers. He told them to do their duty and not to abuse their authority. He didn't tell them to quit being soldiers.
I agreed with his view before I read this, but I found he was able to articulate them much better than I could.