No, if war was NOT a necessity, no creature would have achieved sentience.
war thins the population. it's a force of nature. it makes those with desirable traits (strong, smart, agile.) those who can generally survive war, carry on their genes.
now, the thinning of the population. without war, the world would be overcrowded. it's crowded now, but without war it would be much worse. war is a handicapant to over-population.
at you statement of that no creature would gain sentience, that is complete bullstuff. war is the reason why the USA, Russia, and Britain among many are still here today. the fights between species, and the outcome of mammals and humans over other species of mammals is the reason why we're here.
There is a difference between war and survival. All of the points you brought up were about the natural survival of things. Predator, prey, natural selection; all were mentioned in your post. I am talking about war, the massive slaughtering of thousands of men who had no previous disputes with the soldiers that they are killing/are being killed by. War, the basis for global issues. War, the man-made force that if not ended, will put an end to man; as Kennedy said.
I'm not here to argue with you, war is not a necessity in human life, it never will be.