One key thing I noticed was this; The tribes are expanding consistently while at the same time "waging" a war.
How? These states are involved in a multi-generational total war, but have the time, resources and interest to maintain colonization? I think it would be key for the simulation to represent the deeper socio-economic aspects of warfare. To be in a state of war for pre-modern states is to push the systems and institutions of that state to its limit for one purpose.
In reality, if a tribe were at war, men would be called forward, away from farms and hunting, building, colonizing, in order to fight. Warfare is expensive, and a very very uncertain state of operation for polities, all the energy and resources pent up from peace is put forth into a single concerted effort. Even then, victory is not guaranteed. The state which diverts too much effort from the war is very likely to collapse from defeat, and the state which can maintain a focused fight is likely to win.
I think that the simulation should also represent just how considerable of an effort it is to wage war (when warfare is implemented), And just how random and unknown the results of that war can be. States collapse, culture changed, a golden age or a dark age, and not just for the polities involved in the war too. Warfare and its results are a ripple, cities burnt, trade routes closed or gone, people migrate, new technologies. These changes are felt globally, even in pre-history. A single war, can be the ripple that leads to the collapse of an empire hundreds of years later, or an entire historical era. For example, the rise of the Huns and their reputation combined with climate changes led to mass migrations which led to the collapse of a decaying Western Roman Empire and therefore resulted in the dark ages until the mid 900's. That led to the creation of the modern European nations.
Think of war as part of a toolkit, an operational mode available to these polities to keep itself alive, to achieve a better state, and to maintain status quo.