re: preemptive war
I wouldn't rule out preemptive war, even the unexercised threat of it can be a strong deterrent to evildoers. But if it is done, it had better turn out to be justified.
As for going to war solely because it improves your geopolitical position or your tactical situation, that is the very definition of aggression. We went to war in Iraq in 2003 because we felt it would give us a tactical and strategic advantage. We went to war in Iraq in Desert Storm to DENY Saddam that same advantage. The justifications were WMD, and the rape of Kuwait, but those were not the reasons.