In our current world there is rather blatant and easy justification for war. I don't know what world you live in, but you sound like someone who's never stepped out of their own living room. Things can look relatively easy from a living room window.
Here's the easy justification for war: there are people in this world who do not hold any reservations about using violence to get what they want. In many instances of this the offending party can be stopped without resorting to violence, but in cases which happen all to often the only way to stop them is by reciprocating the violence.
There's similar justification for secrecy; there are many people in this world who hold no reservations about exploiting vulnerability.
Do I believe this justifies the situation? No. I don't. But we can't change the past, or undo other people's wrongs. The situation is what it is. If you feel being there was an injustice, fine. Punish those involved, but with the situation given it would be equally wrong to leave a devastated state to be exploited. That would be at LEAST equally unjust, if not more so.
There are many, many people who see the military as a direct way of helping the most vulnerable people defend themselves against the most violent. These people get to make a positive impact on others' lives which is on orders of magnitude greater than they could otherwise.
So while I agree with you that there ought not be war, just like there ought not be violence, I don't foresee a future where there will be no war or violence.
