A NASA-funded study looked at factors that cause a civilization to collapse. In the past 5,000 years, many advanced societies have collapsed, resulting in hundreds of years of decline and regression. Basing their model on how predators and prey interact, the scientists concluded that societies that collapsed had two factors in common: overconsumption of natural resources and economic stratification.
The so-called "balance of nature" works like this: As a prey population grows, the predators that feed on them thrive as well. But once the predators become too numerous and overconsume the prey, famine results. The predator population declines as well (a “collapse”).
The study looked at three scenarios: Egalitarian, Equitable and Unequal. In an Egalitarian society that has no elite class, an equilibrium can be reached where the commoner population increases to the maximum carrying capacity of the planet.
However, if the population overconsumes its resources, a collapse results from which there is no recovery. Resources, wealth and population all go to zero.
The Equitable society divides the population into “workers” and “nonworkers.” This society can reach equilibrium with slow growth and fairly distributed salaries.
In the Unequal scenario, the population collapses after an apparent equilibrium when the elite population starts to take off, peaking around year 775. By year 900, everything has collapsed, and nature makes a recovery.