Listen to part of lecture in an anthropology class.

One of the big questions when we look at prehistory is: Why did early state form?Well, to begin we'd better define exactly what we mean when we've talk about the states. The human groups that are the smallest and have the least social and political complexity, we call bands. The groups that are the largest and most socially and politically complex, we call states. So, the level of complexity here refers to the organization of people into large, diverse groups, and densely populated communities. And there are four levels in total: bands, tribes, chiefdoms and states.  

But, but back to my original question.Why did early states form? Why not just continue to live in small groups?Why become more complex?

One theory called the environmental approach hypothesizes that the main force behind state formation was population growth.  It assumes that centralized management was critical to dealing with issues caused by sudden population surges, like a strain on limited food supplies. 

At the least complex end of the spectrum, the few families living in bands are able to meet their own basic needs.They usually hunt together and forage whatever foods are available to them, instead of domesticating animals and planting crops. In order to efficiently take advantage of the wild foods available, bands are often nomadic and move around following herds of animals. This strategy is feasible when you have a small population.

But when you have a large population, well, the whole population can't just get up and move to follow a wild herd of animals. So you need sophisticated technologies to produce enough food for everyone. And there is an increase need to resolve social problems that arise as people begin to compete for resources. To manage intensified food production, to collect, store and distribute food, you need centralized decision-making, centralized decision-makers. 

It's the same thing when it comes to maintaining social order. You need to create and efficiently enforce a formal legal code.It makes sense to have a centralized authority in charge of that, right? So a hierarchy forms.By definition, states had at least three social levels. Usually, an upper class of rulers, a middle class comprised of managers and merchants, and a lower class of crop producers and agricultural laborers. 

The environmental approach hypothesizes that states appear in certain environmental settings, settings which have a severe population problem or a shortage of agricultural land. But not everyone agrees with the theory.It definitely has some weaknesses.For example. states have developed in places like the mild lowlands of Mesoamerica and in Egypt's Nile River Valley. Both places had vast areas of fertile farmland, no shortage of agricultural land. And what about population increase? Well, there were some early states that formed where there wasn't any sudden population increase. So it seems that these are valid criticisms of the environmental approach.