I was reading von Clausewitz last week. I didn't get much out of it, frankly, but I decided it had been collecting dust for too long. What I was really struck by was the opening:

We must first define war. We shall not begin with a pedantic definition, but confine ourselves to wasr's essence: the duel. War is nothing but a duel on a larger scale. If we would unite in one conception the countless uels of which it consists, we should imagine two wrestlers. Each seeks by physical force to overthrow the other, render him incapable of further resistance, and compel his opponent to do his will.

War is thus an act of force to compel our adversary to do our will.

He goes on to speak of how the use of force has no theoretical limits and that the side which does not limit it's brutality will thus have an advantage.