The classic just war doctrine as articulated by the Church does not view all use of force as evil; rather it declares that war can actually be a positive act of love entirely consistent with the character of God. Love of God and neighbor impels Christians to seek a just peace for all, especially for their neighbors, and military force is sometimes an appropriate means for seeking that peace.~ Dr. Darrell Cole, When God Says War Is Right, p. 7 (my bold)
While I agree generally with Dr. Cole’s assessment of war as expressed in Christian just war doctrine, it is vital that we ask, “Who is my neighbor?”
A lawyer once asked Jesus the same question, trying to find out just how far God expected him to take this “love your neighbor” stuff (Luke 10). But in the context of war, we don’t ask “Who is my neighbor?” to avoid showing mercy and compassion, but rather to determine legitimate jurisdiction in wreaking violence. Binding a neighbor's wounds and putting him up at the inn is one thing. Devastating his community, and killing and maiming countless of his family and friends in the process of “liberating” them, is another thing altogether.
One of the jus ad bellum (“justice in going to war”) criteria is proper authority. I.e., the decision to go to war must be made by the appropriate governing official(s). And of course, where there is authority, there is the matter of jurisdiction — the lawful extent or range of that authority.
St. Paul teaches, “There is no authority except from God, and the authorities that exist are appointed by God” (Romans 13:1). But I am unaware of any scriptural support for the idea that rulers have lawful authority to intervene militarily in other nations, even in a just cause. Dr. Greg Bahnsen stated the matter well in his sermon series A Christian View of War:
[T]he circumscribed area of lawful authority for the state is its own citizens, and not the citizens of another land or another nation.Just war is rooted in the right to defend one's family, community and nation against violent aggression. Inasmuch as men have a civic responsibility, then, to defend their own communities and nations, Cole is correct. Love of God and neighbor should impel Christians to come to their neighbors' defense.
Do nations accrue moral responsibility, in the name of justice, for what happens in foreign regimes? If so, where does God tell us this? Where does God tell us we have the right to intervene in another nation, even in a just cause? And the answer, I think, is that deafening silence — He does not.
Of course, one may legitimately choose for himself to participate militarily in some just cause on foreign soil. But another man — even the president of the world's sole superpower — has no right to choose this for him. Bahnsen continues:
Politicians who choose intervention by war, you must remember, are always expending the lives, money and freedom of others. And they have no right to do that, except where God has authorized. They have no right to take jurisdiction and apply the police, coercive powers of the state [to compel their own citizens' participation], except where God authorizes.And this is where it seems Cole’s recourse to “love of God and neighbor” may be unduly overbroad — an attempt, perhaps, at justifying foreign military adventurism in the name of Christian compassion.