Population has always been a critical driver of events and prior to the Industrial Revolution we lived in a zero sum world, with energy and resources effectively limited to that which could be harvested from photosynthesis, one person’s gain was at the limit, always someone else’s loss. Very low density hunter gather populations could thrive (often quite nicely) because they rarely approached their local resource limits, but the invention of agriculture changed this dramatically. The next 10,000 odd years of recorded history is a long story of local competition for fundamentally constrained opportunities. There were only three ways to survive and dominate, use what you had more efficiently, take what someone else already had, or move to somewhere not yet occupied. One drove warfare, conquest and empire, the other drove innovation and intensification … yet the diffuse and intermittent nature of sunshine and climate imposed a strict zero sum game on both of these strategies, at least locally.