The condition for defeating an enemy presupposes great physical or moral superiority or else an extremely enterprising spirit, an inclination for serious risk. When neither of these is present, the object of military activity can only be one of two kinds: seizing a small or larger piece of enemy territory, or holding one’s own until things take a better turn. The latter is normally the aim of a defensive war. . .
The possibility that a military objective can be modified is one we have treated hitherto as deriving only from domestic arguments [Book VI Ch 8], and we have considered the nature of the political aim only to the extent that it has or does not have an active content. From the point of view of war itself, no other ingredient of policy is relevant at all. Still, as we argued in the second chapter of Book I (purpose and means in war), the nature of the political aim, the scale of the demands put forward by either side, and the total political situation of one’s own side, are all factors that in practice must decisively influence the conduct of war.
This post links this concept of “serious risk” with “surprise”, which is one of the keys to success in the tactical/operational attack, but then highlights the overall importance of the political purpose to which the military aim is subordinate.