One of the conclusions that Carl von Clausewitz reaches in his study On War is that the defence is the stronger form of war. (There are only two forms, hence the comparative tense.) Many of my students have found this difficult to understand, especially if they were American and raised on the idea that the ‘best defence is a strong offence.’
“The defensive form of war is not a simple shield, but a shield made up of well-directed blows.” (On War, Book Six, Chapter 1)
Clausewitz’s conclusion is beautifully illustrated in the current Russo-Ukrainian War. The defender is mauling the attacker, causing horrendous casualties and losses, but what does this mean? Can Ukraine win the war by remaining on the defensive? The answer is yes, but there are several key considerations. What does ‘winning’ entail? The cessation of conflict may not bring victory. Will Ukraine be able to impose any sanctions on Russia for its murderous invasion? Will the cessation actually involve peace or will it result in another version of North/South Korea or PRC/Taiwan? And so on.
The issue to appreciate is that the stronger form is not the decisive form. The defender wins by not losing but that is not decisive. Ukraine could bleed the Russians to the point where they simply give up, as they did in Afghanistan. That may allow Ukraine to resume some sort of normalcy but it is in no way decisive. Russia may simply re-attack. When President FD Roosevelt opted for unconditional surrender of America’s enemies, it was decisive. Arguably, the Germans and the Japanese (the Italians surrendered in ’43) might have considered an armistice but the Americans and British were not interested. Utter devastation was necessary to convince them that they had LOST, and they had to admit it, and that could only be achieved by an overwhelming offensive.
So, to conclude, the defence is the stronger form of war but the offence is the decisive form.