As described in Tainter's
Collapse of Complex Societies, societies become more complex as they try to solve problems. Social complexity can be recognized by numerous differentiated and specialised social and economic roles and many mechanisms through which they are coordinated, and by reliance on symbolic and abstract communication, and the existence of a class of information producers and analysts who are not involved in primary resource production. Such complexity requires a substantial "energy" subsidy, meaning the consumption of resources, or other forms of wealth. When a society confronts a "problem," such as a shortage of energy, or difficulty in gaining access to it, it tends to create new layers of
bureaucracy,
infrastructure, or social class to address the challenge. Tainter, who first identifies seventeen examples of rapid collapse of societies, applies his model to three case studies: The
Western Roman Empire, the
Maya civilization, and the
Chaco culture. As Roman agricultural output slowly declined and population increased, per-capita energy availability dropped. The Romans "solved" this problem by conquering their neighbours to appropriate their energy surpluses, as metals, grain, slaves, other materials of value. As the
Empire grew, the cost of maintaining communications, garrisons, civil government, etc. grew with it. Eventually, this cost grew so great that any new challenges such as invasions and crop failures could not be solved by the acquisition of more territory. Intense, authoritarian efforts to maintain cohesion by
Domitian and
Constantine the Great only led to ever greater strain on the population. The empire was split in two, of which the western soon fragmented into smaller units. The eastern half, being wealthier, was able to survive longer, and did not collapse, but succumbed slowly and piecemeal, because unlike the western empire it had powerful neighbors able to take advantage of its weakness. It is often assumed that the
Decline of the Roman Empire in the west was a catastrophe for everyone involved. Tainter points out that it can be seen as a rational preference of individuals, many of whom were better off. Tainter notes that in the west, local populations in many cases greeted the barbarians as liberators. ==Diminishing returns==