It occurs to me that societies go through a cycle.

First they are fairly nomadic and aggressive in nature, expanding by conquest and subjugation. Then when they have a bit of land, people start settling it, which leads to agriculture, then a division of labor that allows people to spend more time on intellectual pursuits. Now that the society is making more efficient use of it’s land, it has less need for conquest. Because the society is becoming more intellectual it has less desire for conquest. There is an inevitable shift of energy away from aggression towards more peaceful advancement of the society, leading to a golden age. The golden age declines when the society becomes spoiled by it’s advancement and loses touch with the reality of it’s lifestyle. Then it is conquered by an aggressive society.

That’s how I see it from where I’m sitting anyway.