Prof. Diamond explained that the well being of the advanced societies on Earth continues to deteriorate. Strong evidence is obvious indicating we are headed for greater chaos in our lives.

He estimates that civilized man has less than 30 years to correct our course toward destruction. Will we make the needed changes? He believes the odds are only 52% to 48% that we will succeed.

Duane Nichols

In the prologue to his book, Jared Diamond summarizes his methodology in one paragraph:

This book employs the comparative method to understand societal collapses to which environmental problems contribute. My previous book (Guns, Germs, and Steel: The Fates of Human Societies), had applied the comparative method to the opposite problem: the differing rates of buildup of human societies on different continents over the last 13,000 years. In the present book focusing on collapses rather than buildups, I compare many past and present societies that differed with respect to environmental fragility, relations with neighbors, political institutions, and other “input” variables postulated to influence a society’s stability.

The “output” variables that I examine are collapse or survival, and form of the collapse if collapse does occur. By relating output variables to input variables, I aim to tease out the influence of possible input variables on collapses.

Diamond identifies five factors that contribute to collapse: climate change, hostile neighbors, collapse of essential trading partners, environmental problems, and failure to adapt to environmental issues.

He also lists twelve environmental problems facing humankind today. The first eight have historically contributed to the collapse of past societies:
>> Deforestation and habitat destruction
>> Soil problems (erosion, salinization, and soil fertility losses)
>> Water management problems
>> Overhunting
>> Overfishing
>> Effects of introduced species on native species
>> Overpopulation
>> Increased per-capita impact of people

Further, he says four new factors may contribute to the weakening and collapse of present and future societies:
>>> Anthropogenic climate change
>>> Buildup of toxins in the environment
>>> Energy shortages
>>> Full human use of the Earth’s photosynthetic capacity
Diamond also writes about cultural factors, such as the apparent reluctance of the Greenland Norse to eat fish.

The root problem in all but one of Diamond’s factors leading to collapse is overpopulation relative to the practicable (as opposed to the ideal theoretical) carrying capacity of the environment. The one factor not related to overpopulation is the harmful effect of accidentally or intentionally introducing nonnative species to a region.

Diamond also states that “it would be absurd to claim that environmental damage must be a major factor in all collapses: the collapse of the Soviet Union is a modern counter-example, and the destruction of Carthage by Rome in 146 BC is an ancient one. It’s obviously true that military or economic factors alone may suffice”.

https://en.m.wikipedia.org/wiki/Collapse:_How_Societies_Choose_to_Fail_or_Succeed