When people disagree and cannot resolve their differences amicably, then almost inevitably they will resort to force and violence. The Just War theory was developed to deal with such instances--sadly far too frequent--when people felt they had reached the end of their tether.

In the view of Christian moralists, war is always evil but there may occasions when it will be the lesser of two evils as, for instance, in the case of a Hitler chucking people into gas chambers and ovens. Going to war to stop this egregious evil is then considered to be the lesser evil and would even be regarded as a moral obligation. But going to war would be a last resort.

When is a war then justifiable? The Just War theory lays down a list of conditions which, if satisfied, would make the war justifiable and so just. Some of these conditions are:

Have you exhausted all peaceful means of resolving the problem?
Are the chances of success good?
Will the situation be better after the war than before?
If yes, then only a legitimate authority has the right to declare war.

In terms of this theory, the US invasion of Iraq was immoral as some of us declared before it happened. Not all peaceful means had been exhausted. The UN Inspectors asked for a little more time to establish beyond doubt the existence or not of the so called WMD. The US conceded it was not the legitimate authority by itself seeking the approval of the UN Security Council.

As for success and a better situation after the war, well virtually everyone now agrees that it was a disastrous decision to go to war. God help us.