Essentally combat is an expression of hostile feelings. But in the large-scale combat that we call war hostile feelings often have become merely hostile intentions. At any rate, there are usually no hostile feelings between individuals. Yet such emotions can never be completely absent from war. Modern wars are seldom fought without hatred between nations; this serves as a more or less substitute for the hatred between individuals. Even when there is no natural hatred and no animosity to start with, the fighting itself will stir up hostile feelings: violence committed on superior orders will stir up the desire for revenge and retaliation against the perpetrator rather than against the powers that ordered the action. It is only human (or animal, if you like), but it is a fact.

Author: Carl von Clausewitz