I agree though that economic concerns and fear tend to be the motivating factors for us to take action.
That said, that while economics and fear are motivators...it does not mean the war is unjust...it might simply be the motivator that forces us to take action.
I think the original discussion dealt with the base concerns and ethics of the warrior.
What is interesting to me is how the factors that govern the use of deadly force on the part of individuals is so different from what we do when it is used on a national and international level, For instance, if another person had a business whose success threatened your own business, it would be considered murder and immoral if you went next door and killed him. Yet, on the international level, this happens all of the time.
An individual cannot attack another individual just because he thinks he "might" be a threat. Yet we use that as justification on a national level. Pre-emptive war is ok for nations but is completely illegal on the individual level.
If I decided that it would be in my personal interest to have your house and yard added to my own, it would be illegal and immoral if I went to your home and killed you and took you property. Yet this has been done over and over by the nation and is treated completely differently by most people.
We do things all the time as nations that we would consider highly illegal and immoral if done by an individual and we tell ourselves that our soldiers, the folks who actually do the bidding of the folks that make these decisions are acting legally and morally when doing the very things that we would put an individual in jail for.
Governments would have a hell of a time if they allowed everyone to decide for themselves about the morality of its actions. So we have all sorts of concepts that are used to remove the idea of personal responsibility for ones actions if they are done on the orders of the state. Duty, obedience to authority, etc is crucial in getting people to suspend their individual sense of what is right and wrong.
Look at how much propaganda is needed to get the populace to buy into our wars. That's how we convince ourselves that what we are doing is ok. When the soldiers doing the killing start to lose that sense of rightness you have a situation like we had in Viet Nam where grunts fragged officers who were too gung ho and whole units would find ways to not do what was being ordered.
I actually think that Smedley Butler had it pretty spot on. The public pretty much knows when it is really threatened or not. I think that you could say that the real moral justification for a war is inversely proportional to the amount of propaganda it takes to convince the public to support it. Iraq being a good case in point...