I got kind of tired of avoiding the topic of Pacifism, so I did a bit of research, and stumbled upon some interesting stuff. I'll try to explain in a slipshod manner and be as confusing as possible. As far as I understand it, all of Christendom agrees that the ideal state for a given government is peace.

Pacifism takes this assumption a step further and asserts that under no circumstance is violence justified. Note that non-violence does not necessarily entail non-resistance; think Ghandi. Matt 5:39 "But I tell you, Do not resist an evil person. If someone strikes you on the right cheek, turn to him the other also."

Just War Theory, however, is developed based on the assumption that there are exceptions (other than God telling Isreal to go wipe out some folks) to the non-violence rule. The most accessible example of this is the scenario where you walk into your house and see your spouse being beaten/raped by somebody, and you are forced with the decision to either do nothing (considered a sin by these folks) or resort to violence to stop the attackers. As far as I can tell, there are two branches of Just Warriors in the Christian tradition, the Realists after Reinholt Neihbur who think that the Sermon on the Mount is basically undoable and so violence is just a reality of our sinful selves, and then those that believe under special circumstances violence is not considered a sin at all. Regardless, these guys seem to agree on a set of criteria for determining whether or not a war is justified:

1) Just Cause (self-defense or defense of another party)
2) Right Intention (matching the actual motives for going to war with the just cause)
3) Right Authority (War is declared by a publicly recognized authority who has both the power to mobilize armed forces and the ability to evaluate whether other jus ad bellum criteria are met)
4) Reasonable Hope of Success (avoiding wars that cannot be won and will only cost additional human lives)
5) Last Resort (trying every form of resolution short of direct violence first)
6) Announcement of Intention (stating reasons for going to war with the other side)
7) Proportionality (balancing probably losses and costs for all parties against probable benefits)

The reality, however, is that wars are extremely complex things and it's pretty much impossible to hold conflicts up to these criteria.

Just Peacemaking Theory, however, is a reframing of the question. Instead of asking whether or not war is ever justified, these guys say that because peace is the ideal, how do we go about reducing the probability of war? They met in 1998 as a group of scholars and put together ten (why is it always ten?) "proven" methods for reducing the probability of violent conflict:

1) Support nonviolent direct action.
2) Take independent initiatives to reduce threat.
3) Use cooperative conflict resolution.
4) Acknowledge responsibility for conflict and injustice and seek repentance and forgiveness.
5) Advance democracy, human rights, and religious liberty.
6) Foster just and sustainable economic development.
7) Work with emerging forces in the international system.
8) Strengthen the United Nations and international efforts for cooperation and human rights.
9) Reduce offensive weapons and weapons trade.
10) Encourage grassroots peacemaking ad other associations.

Anyhoo, hope you find this mildly interesting.