What problems from within and from outside invasions spell the end for most civilizations?

Answer 1

According to a 2014 published research paper, 'Human and Nature Dynamics (HANDY): Modeling Inequality and Use of Resources in the Collapse or Sustainability of Societies' by University of Maryland researchers Safa Motesharrei and Eugenia Kalnay, and University of Minnesota's Jorge Rivas, there are five (5) risk factors for societal collapse. These factors are:

1. population, growing size and location,
2. climate
3. water
4. agriculture
5. and energy
   

In addition, (quote), Motesharrei's report says that all societal collapses over the past 5,000 years have involved both "the stretching of resources due to the strain placed on the ecological carrying capacity" and "the economic stratification of society into Elites [rich] and Masses (or "Commoners") [poor]." ... Elite power, the report suggests, will buffer "detrimental effects of the environmental collapse until much later than the Commoners," allowing the privileged to "continue 'business as usual' despite the impending catastrophe."(Source: NASA Study Concludes When Civilization Will End, And It's Not Looking Good for Us by Tom McKay March 18, 2014. News.mic.com)

(Quoted): As of last year, humans are using more resources than the Earth can replenish and the planet's distribution of resources among its terrestrial inhabitants is massively unequal. This is what happened to Rome and the Mayans, according to the report." [McKay]... historical collapses were allowed to occur by elites who appear to be oblivious to the catastrophic trajectory (most clearly apparent in the Roman and Mayan cases). [Motesharrei]

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When these factors come together as a perfect storm, there will certainly be strife and tensions between the ordinary people of a town/city, region, State, and Country. In 2016, we have such high tension among the masses including:

1. mass shootings - record 50 dead in Florida 2016 -- But mass shootings started first, at least in the US, with the US Post Office in the 1970s, hence the description, "going postal"
2. knife attacks - most recently June 2016 in CA
3. crimes against other citizens
4. crimes against specific groups

These are in addition to terrorism from both inside and from outside.

The article goes on, (quoted): Writes Nafeez Ahmed at The Guardian:"Although the study is largely theoretical, a number of other more empirically-focused studies — by KPMG and the UK Government Office of Science for instance — have warned that the convergence of food, water and energy crises could create a 'perfect storm' within about fifteen years. But these 'business as usual' forecasts could be very conservative.

"NOTE: (quoted) : NASA has issued a clarification about its role in the study, saying that while the study relies on NASA research tools developed for another project, it did not directly solicit, direct, or review Motesharrei's paper. "As is the case with all independent research, the views and conclusions in the paper are those of the authors alone. NASA does not endorse the paper or its conclusions."

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Though this information sounds pretty bleak for today's world, especially considering that the authors of the study predict world societies' collapse within 15 years, the reality is that every resource we have on earth is finite. Despite salt-laden oceans, many areas lack rain and drinking water. Climates are changing drastically (global warming), and weather patterns seem askew (droughts vs flooding). More US acres are being consumed by fires due to hot weather and no rain, while undeveloped countries add to air pollution by "slash and burn" agricultural practices. These are in addition to other threats, like earthquakes, volcanic eruptions, etc. All of these create financial burdens on public and private resources.

Humanity can only bear these stresses for so long before--something needs to change. Yet, no one government or group can possibly change ALL the problems, so we all need to change our consumption of resources and how we each protect our planet.

Answer 2

Cities