Agricultural revolution
By actively managing their food supplies, agricultural societies were able to produce more food than hunter-foragers and support denser populations. Having a large population nearby made it worthwhile for farmers to grow more food than they needed for themselves, as they could trade this surplus for other goods. For non-farmers, this meant that they could focus on making other goods and trading these goods for food and other things. People could specialize—focus on doing one thing—which led to increased productivity. Increased productivity led to the creation of better buildings, tools, weapons, and also to the rise of governments to oversee this activity and military forces to protect people and resources.Many population centers evolved into the first wave of city-states that emerged within a few thousand years of the agricultural revolution. Eventually those states began to have complex bureaucracies to tax and administer their people, a significant catalyst for the birth of writing, which was transformational for civilization.