For hunter gatherers it wasn't easy to stockpile enough long term storage portable food to take to war, nor could you predict periods of bounty (which is why so many ancient cultures had prohibitions to making war during winter that almost no one broke) to plan long term campaigns. This style of sustenance also kept nomadic band population low as following the herds and the reduction of ease of hunting and complications in moving gave significant advantage to smaller social units.

We see a radical increase in social group size with the advent of agriculture, eventually leading to more permanent town and eventually city living instead of nomadic bands as you generally needed to be in one place to keep others from taking your crops and tending them year round.

I fully understand that there are a lot of luxuries and even just basic life improvements that wouldn't be available to us if we had kept as small hunter gatherer bands, and maybe a lot of people alive now couldn't survive or thrive in that kind of environment, it would be a very, very different world than what we know today but one thing I do know is that of we had never discovered agriculture we would never have eventually become a species that could kill off 95% of the life on the planet with the press of a button.