Fortunately we don't know the might-of-beens ... just the what-was. Would things have been better if Alexander had lived, conquered both India and Italy, so that Indian and Roman civilization were cut off? One counter-historian has said that in that event, history would be 1000 years more advanced today, than it is ... with Buddhism not Christianity as the dominant religion, no Islam and no Judaism either. And progressive that this guy is, that we would be 1000 years more advanced in outer space, and already colonizing other solar systems.
It is not clear to me, that being conquered by nearly tribes is any better than being conquered by far away tribes. Back in the day before WW II, war was considered part of everyone's alternative business plan. Ultimately trial by combat is at the top of the chart, followed by trial by ordeal, and finally trial by court. The idea that everyone will play nice, and stick to trial by court ... is naive. Trial by ordeal includes such fun things as plagues and starvation. I think the only lesson that can be drawn is ... don't let other tribes conquer you, and that sometimes a good offense is the best defense.