All military action is unjust.
Except when a nation must defend itself against another nation's aggression; to be without a military is to have a big sign that says "please invade us", much the same way anti-gun legislation puts a sign on the citizen's face that says "please mug me."
I don't consider myself part of a "nation" in the way you use it. Self-defense is important, but so are the lines that we choose to draw. If a superpower attacks the US tomorrow, I surely won't support the US army in anything that it does -- how could I, considering history? I will defend myself and my community -- fuck this country. I just hope that someday, the US won't exist.