I often wonder about this. Large scale wars I believe only occurred with the development of agrarian based societies. Nomadic societies would usually not risk all in a do or be enslaved war. Nomadic tribes frequently raided each other but could retreat and make do if necessary.

Farms had to be defended. It would take years to restore a destroyed farm and what would you eat if the enemy stole your harvest and all your animals.

My guess is such a winner take all scenario, they were not merciful to the women and children either. They killed those who resisted and enslaved the rest.