Spartan woman giving a shield to her son  (credit: Le Barbier, via Wikimedia Commons)

At the same time, their neighbours, the Spartans, were evolving their society, the perfect military state. The clash called the Peloponnesian War became inevitable, and Athens lost. A few years later, the Macedonians out-did the Spartans, and after another generation or two, the Romans ended the matter by conquering them all. 

In each case, a worldview, a set of attached values, and a set of behavior patterns, all blended into a culture, were tried against that culture's neighbors and proved just a little bit more vigorous. Evolution by constant testing and gradual increments, the same as in the genetic domain, kept bringing a new human social system to the top of the cultural food chain. Harsh. Real.  

And note also how cultural evolution by variation and selection of memes rather than genes is tenuous and scary, but also much faster and more responsive than is evolution by the genetic model. We can adapt to a changed set of weather patterns and grow a new kind of crop and live off of it because we can watch, form concepts, build mental models of reality and re-boot our way of life. In a generation or two. Not blindingly fast, but much faster than the genetic mode of evolution. Human. 

For better or worse, we not only adapt to changes in our environment (which always come), we also do it in a few generations. In the genetic, Darwinian mode of evolution, a few generations-long time span is nearly meaningless. In the human, cultural mode of evolution, what we call an "era" can be less than five generations. That kind of change fits the term revolutionary. It overturns almost every aspect of a tribe's life.