This section is of particular interest:
According to Joseph Tainter, a professor of environment and society at Utah State University and author of The Collapse of Complex Societies, one of the most important lessons from Rome’s fall is that complexity has a cost. As stated in the laws of thermodynamics, it takes energy to maintain any system in a complex, ordered state – and human society is no exception. By the 3rd Century, Rome was increasingly adding new things – an army double the size, a cavalry, subdivided provinces that each needed their own bureaucracies, courts and defences – just to maintain its status quo and keep from sliding backwards. Eventually, it could no longer afford to prop up those heightened complexities. It was fiscal weakness, not war, that did the Empire in.
So far, modern Western societies have largely been able to postpone similar precipitators of collapse through fossil fuels and industrial technologies – think hydraulic fracturing coming along in 2008, just in time to offset soaring oil prices. Tainter suspects this will not always be the case, however. “Imagine the costs if we have to build a seawall around Manhattan, just to protect against storms and rising tides,” he says. Eventually, investment in complexity as a problem-solving strategy reaches a point of diminishing returns, leading to fiscal weakness and vulnerability to collapse. That is, he says “unless we find a way to pay for the complexity, as our ancestors did when they increasingly ran societies on fossil fuels.”
Also paralleling Rome, Homer-Dixon predicts that Western societies’ collapse will be preceded by a retraction of people and resources back to their core homelands. As poorer nations continue to disintegrate amid conflicts and natural disasters, enormous waves of migrants will stream out of failing regions, seeking refuge in more stable states. Western societies will respond with restrictions and even bans on immigration; multi-billion dollar walls and border-patrolling drones and troops; heightened security on who and what gets in; and more authoritarian, populist styles of governing. “It’s almost an immunological attempt by countries to sustain a periphery and push pressure back,” Homer-Dixon says.
Meanwhile, a widening gap between rich and poor within those already vulnerable Western nations will push society toward further instability from the inside. “By 2050, the US and UK will have evolved into two-class societies where a small elite lives a good life and there is declining well-being for the majority,” Randers says. “What will collapse is equity.”