"More ambitious projects need a certain critical mass of resources behind them. Ancient Egyptian civilization built a large irrigation system to make the best use of the Nile floodwaters for agriculture, a feat that would not have been possible to a small tribe or chiefdom."

Yes, a small tribe couldn't have enslaved large groups to form the majority of the labor base. Societal advances are easy to achieve if you usurp resources from a marginalized group and force them to work on your projects. I would hope that we have learned that's not the right model to pursue.