A rather cynical one.
When I read just war theory, as a teenager, the most important point, I determined (in this rarefied and rarely consulted domain of thought), was this:
In contemplating intervention into a conflict with which one’s own country is not directly involved, it is not enough merely to determine which side is more nearly in the right. One must also have good reason to believe that, by intervening, one’s State could win and establish a stable and just peace.
Even if you know who is in the wrong, if there is no likely way of “winning,” or if one’s intervention is not likely efficacious to establish a peace, entering into the conflict is immoral.
A recent study of just war theory and history by Laurie Calhoun suggests that most uses of the tradition, especially in recent times, have been to cover for gross, murderous immorality. Not to limit warfare.
As near as I can make out, this is largely because the tradition is almost never treated seriously or rigorously in the manner indicated above.
It is telling that I have not once heard, in recent public discussion over the Syrian intervention, one mention of just war theory.