Why

The difference between war and the fighting that preceded it was in the numbers of human beings who took part. Fighting had formerly been done by individuals or small groups. Before agriculture larger numbers could not come together and stay together long enough to carry on war. Their life made that impossible because it kept them dispersed.

Fighting shaded into war. Human beings did not suddenly go from fighting as individuals or in small groups to fighting in large numbers. The increase in numbers took place gradually. It had to start before agriculture – as soon as human beings could accumulate some food. But it could not go very far so long as the human species relied on hunting. The big increase could come only with agriculture. That introduced war, as war has been commonly understood.

Once human beings could fight in larger numbers they had to because the outcome of the fighting was determined – generally – by numbers. The human beings in one agricultural area could not successfully attack another area or defend their own unless they equaled or exceeded their enemies in numbers. If they failed to come together and stay together in sufficient numbers for fighting, they lost. What constituted sufficient numbers depended upon what numbers their enemies could muster. The more of their enemies, the more they had to be.

Numbers determined the outcome generally, not exclusively and always. They determined the outcome only if the human beings who fought were otherwise generally equal – in weapons, strength, skill, intelligence and determination. Human beings who fought were generally equal in these other matters that affected the outcome. This was because they usually came from the same area and had access to similar resources and resembled one another physically. Their individual differences in these other matters tended to average out because of the numbers involved. So numbers were generally decisive. Sometimes fewer human beings would defeat more. But that happened less frequently the greater the difference in numbers – and it did not happen at all if the difference was great enough.

So numbers were indispensable once they became possible. Human beings had to fight after the introduction of agriculture just as they had to fight before. That was because of the situation life put them in – and put all other species in. The difference was that with agriculture more human beings could fight together at one place and at one time. And because they could fight like that they had to.