@FeserEdward makes a convincing argument that we must in conscience oppose any war that does not CLEARLY satisfy just-war standards. “If the war does not meet the standard of moral certainty, then we can be certain that we must oppose it.”

To which I would add that this is especially true of a pre-emptive war. If you propose to start a war because you are persuaded that the enemy is about to attack, you must be morally certain that the attack is imminent. If you’re wrong, YOU are the aggressor.