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 an ever greater strain on the population. The empire was split into two halves, of which the western soon fragmented into smaller units. The eastern half, being wealthier, was able to survive longer, and did not collapse but instead 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 collapse of the western Roman Empire was a catastrophe for everyone involved. Tainter points out that it can be seen as a very rational preference of individuals at the time, many of whom were actually better off. Tainter notes that in the west, local populations in many cases greeted the barbarians as liberators. Diminishing returns Tainter begins by categorizing and examining the often inconsistent explanations that have been offered for collapse in the literature. In Tainter's view, while invasions, crop failures, disease or environmental degradation may be the apparent causes of societal collapse, the ultimate cause is an economic one, inherent in the structure of society rather than in external shocks which may batter them: diminishing returns on investments in social complexity. Finally, Tainter musters modern statistics to show that marginal returns on investments in energy (EROEI), education and technological innovation are diminishing today. The globalised modern world is subject to many of the same stresses that brought older societies to ruin. However, Tainter is not entirely apocalyptic: "When some new input to an economic system is brought on line, whether a technical innovation or an energy subsidy, it will often have the potential at least temporarily to raise marginal productivity". Thus, barring continual conquest of your neighbors (which is always subject to diminishing returns), innovation that increases productivity is – in the long run – the only way out of the dilemma of declining marginal returns on added investments in complexity. And, in his final chapters, Tainter discusses why modern societies may not be able to choose to collapse: because surrounding them are other complex societies which will in some way absorb a collapsed region or prevent a general collapse; the