Prior to that we were hunters and gatherers for 2 million years. Our population was in check with average of 1 baby every 4 years or so. As they had to move often, they could not afford carrying too many babies with them. They had no or minimal possessions, and as such fights were small. Only 5% of people died due to violence.
There was no arthritis, disc disease or many of the current bone conditions at that time. And people were more skilled and therefore smarter (their brain was bigger).
Additionally they now had land and homes, which could be taken from them by others. With more food population exploded. They started to have babies every year. Large scale wars started over food and land. At this time over 50% of deaths were due to violence.
Previously when a tribe was met with other aggressive tribes, they just packed and left when they were hunters and gatherers. After the agriculture age they could not do that as their farms could not be moved. Large scale massacres started to appear in human history.
This caused some individual to offer protection and solders to defend the farmers. Leaders and kings started to appear in history.
Farmers domesticated animals which caused many deaths in human beings due to infection. Large population that stayed in one location meant disease spread quickly. Large number of people were wiped out due to disease from farm animals.
Human beings lived longer as hunter/gatherers. Were smarter, and healthier and we can conclude happier and more in tune with nature. Agriculture age changed all that.
The sole purpose of agriculture age was to increase population, something that our DNA considers success and the main mission of DNA is to duplicate itself at all cost, no matter the cost to health and happiness. That is the sole reason of DNA for being. When DNA doubles in number it considers itself a success.
I find our history fascinating.