I assume the definitions of ‘power’ and ‘authority’ here.
Just war is, in a sense, power applied to bring social order out of
social disorder. War is understood to involve at least two contrary powers. In
order for war to be possible, there must be an order to which both powers
actually belong.
An analogy to war is competitive sports, in which two
opposing teams compete against each other. Each team tries to accomplish two
goals at once; to score points against its opponent and to prevent its
opponent from scoring points against itself. There are intrinsic and
extrinsic common goods proper to each team: Individual athletes must work well
together as a team, and they all share in their team’s victories. There are,
however, common goods proper to the sport in general; goods in which
all teams share even as they compete against each other.
With respect to the intrinsic common goods of the sport, if
there were no rules of play, then there would be no game;
and, if it were not assumed that both teams would honor the rules equally, then
competition would not be possible. As for the extrinsic goods of the game (the
goods for which those who compete), were there none to be enjoyed, there
would be no purpose for playing.
War is similar in the sense that there is an extrinsic common good that is supposedly exclusive to one party in the conflict: viz., the terms of victory and the driving motives for declaring war. However, if there were no fundamental order that was shared by all opposing forces, there would be no war: It would at most look like war, but would more appropriately be called suppression or interdiction if done well; a riot or massacre if not.
So, what is the order that enables man to wage war?
Primarily, man desires to live and to live well. War is waged on this
assumption; that death and needless suffering is to be avoided. However, peoples
wage war by means of those who actively risk death and suffering on their
behalf: The essence of a warrior is to undergo such risk for the sake of
victory.
The relation between the warrior and the authority which empowers him to wage war implies the common nature of victory: Even fallen warriors can share victory. However, the good to which the warrior consecrates himself is greater than the admittedly thin consolation of posthumous victory and honor. If it were not the case that the warrior’s risk is itself a testament to the greatness of his cause, a good that encompasses his whole community, then military service should have no honor attached to it. In other words, if individual life and prosperity is the greatest good to which a man can aspire; if the commonweal is nothing greater than the totality of individual goods; or if the warrior’s moral calculus simply means gambling his life for a greater number of potential beneficiaries, then the warrior is reckless by nature, because such an outcome is far from certain. Rather, it is more likely that not only the warrior suffer, but the whole nation.
The nature of war includes sacrifice for a higher good, viz. the peace and order of the nations involved.
