Answer: perhaps the necessity is not really inherent to any concept whatsoever, and thus just a consequence of general human misbehaviour. Being a consequence it still has some meaning, in this that it may preserve life, however contradictory this may seem. If the human’s first understanding of his own identity inside a whole is given through the defense of a territory, which warrants he may organize himself as it is of his liking, which is to say, warrant of freedom, then war becomes the necessary consequence of his understanding of freedom. Of course you may say that you’re just protecting your property, which is your income, but in the depth it’s more or less the same. The ‘mine’ and the ‘I’ do find easy bridges of communication. Of course you may say, too, that it would be more than enough to deviate armies towards the right place (Prophets in Chronicles) in order to avoid blood sharing, but this kind of wisdom does affect rarely a few human, so that it is of need to do with what there is.
And precisely, war in this that it is war, which is to say an ordered confrontation with some rituals linked to it (war declaration, place of confrontation, rules of confrontation, conditions of confrontation, rules of determination of who the victory, consequences of such a condition, etc), it may still be better than the constant agression in so called times of peace. Put yourself into the following situation: someone insults you while you’re just doing your job and then you are said, not to react because you have to be peaceful and tolerant. Was the other? In this case, you may prefer some kind of ordered confrontation in order to restore some inner balance.
Just take Isaias: « You say peace, peace, but your hearts are full of lies and poison. »
You’ll never determine your own identity if it’s not in a ranged confrontation with the one who is agressing your identity. It reveals the wicked quickly and the coward – but we’re rarely honest.