"When you pray as you ought, there may come into your mind things about which it seems right to be angry with your brother. There is absolutely no anger against your brother which could be justified. If you look, you will find that the question can be settled quite well without anger. Therefore do your best not to be moved to anger."
I think you may be somewhat misunderstanding what we mean by "just" in this context. It is not to say that the "just war" is a positive good, but rather a one in which we may engage without necessarily sinning. It is as opposed to an "unjust war", which is inherently sinful. It is for this reason Pope John Paul II has always preached against warfare: any resort to war, in order to settle some difference between nations, necessarily means that other, less destructive means, have failed. "Just" war is a last resort, not a first option, and is necessarily something that (as you say) is "inevitable ... thrust upon us and .. certainly practice[d] war against greater evils".