Just War...

I was in the presence of a very influential and public Christian figure recently, and while having a discussion, he mentioned that under the New Covenant, or New Testament, he did not see how there could possibly be a "Just War". He had spent considerable time citing the Catholic church on things like abortion and gay marriage, on which we agreed. Several things we did not completely agree on, which is cool. But I was taking my Contemporary International Problems midterm, and we were questioned about the "Just War" Doctrine, that is accepted by the Catholic church and originally came from St. Thomas Aquinas. Here they are:

The war must be started and controlled by the authority of state or ruler.

This means that for a war to be just, only the head of the nation can start it. It rules out civil war and rebellion.

There must be a just cause.

This means that anyone and everyone being fought against must truly deserve it. A just cause would not include greed, revenge or pride, but it would include protection, self-defence and prevention of a worse evil.

The war must be for good, or against evil. Law and order must always be restored.

This means that no one should ever find themselves on the side of evil for any reason, whatever the politics involved. It also means that there is a duty to return to a life of normality after the war is over.

Source: http://www.bbc.co.uk/dna/h2g2/alabaster/A644672