Well I'm afraid to say that you are all quite wrong
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Maybe once war could not be avoided due to primitive social structure (like in the middle ages) but for example the 2nd world war could have easily been avoided by less moral cowardice among the leaders of Europe. But in our modern age of nuclear weapons it is not longer necessary to go to war, just putting a bit more effort into the good ol' diplomacy and thinking of others opinions should do the trick, and other things like economic sanctions and loan withdrawal should work. Anyway if we look at human history it has been marked by progressive liberalising, I daresay that the British would have left America eventually and if Hitler had one ww2 I expect we would have ended up with the same sort of society we have today, as economic forces leading to social and political change drive history ever forward.
Violence always provokes more violence, and that leads to endless violence though human history, always has, always will. You cannot stop violence with violence.