Clausewitz pictures defense not merely as passive, but as consisting of two parts: the first, waiting for the attack, and the second, parrying it, the counterattack. "So the defensive form of war is not a simple shield, but a shield made up of well-directed blows." (357) "Even when the only point of the war is to maintain the status quo, the fact remains that merely parrying a blow goes against the essential nature of war, which certainly does not consist merely in enduring."(370) Defense nevertheless remains negative, for it is not the end for which war is to be fought:
"If defense is the stronger form of war, yet has a negative object, it follows that it should be used only so long as weakness compels, and be abandoned as soon as we are strong enough to pursue a positive object. When one has used defensive measures successfully, a more favorable balance of strength is usually created; thus, the natural course in war is to begin defensively and end by attacking. It would therefore contradict the very idea of war to regard defense as its final purpose...." (358)Moreover, although the defense has the advantage of its object to preserve, it suffers from a serious psychological side effect, namely that a defensive retreat or loss of territory can cripple domestic and military morale. The armed services and population cannot be expected to "tell the difference between a planned retreat and a backward stumble." (471) Psychological factors impede defense as well as offense.
In addition, perhaps the criteria for the advantage of defense over offense have altered since Clausewitz' day. Although his arguments still seem valid in the context of conventional warfare, they appear less credible with regard to nuclear weapons, for which no country currently has an effective defense. Thus, Clausewitzian defensive doctrine probably needs to be reassessed in light of nuclear arsenals.