Agriculture is a different history. Means big cities with big walls, easy to defend. Agriculture and farming can feed much more people so you can have a bigger army and bigger buildings with enough room for harvests (so you don't need to move in winter). Hunters/gatherers can conquer and enslave for a while but can't feed all people, and dissolve in smaller groups when reaching a critical point.
The same principle applies to the army that can conquer, but would not survive at long term without the civils that create the foods and services.
https://www.insidehighered.com/news/2010/11/30/anthroscience
You can now study ancient DNA as an alternative method of studying ancient history. It seems there was a lot of killing of males and capturing females leading to population replacement.