I don't go looking for causes. Members here have predicted 137 of the last 0 collapses. It's simply not something that rewards me. There are billions and billions of variables, any one of which can alter the situation. (See Chaos Theory, below).
Far better to prepare for needs than to try to predict something that's not predictable. In virtually all scenarios--billions of them--you're going to need water, food, hygiene supplies, light/heat/cooking fuel, first aid/medical, and defense. Those are where people should concentrate their efforts, IMO.
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Long before I began prepping I read
Lucifer's Hammer by Niven and Pournelle. I was blown away by it--realistic, the sociological ideas in it are plausible, and the responses to a comet hitting the earth were reasonable.
So I began to think of the prepping problem in terms of that kind of scenario. Among the things I believed was that I needed to lie low for 6 months to a year and then emerge, once the aftereffects of "the collapse [tm]" had run their course for the most part.
Talk about being a singular scenario-planner. I was the regional representative for scenario-planning!
But eventually I realized that should this one very specific scenario not come to pass, I'd be in a world of hurt. Fact is, there is an unlimited number of possible scenarios and nobody can anticipate them all. Will a charismatic leader emerge who rallies people to a brighter future? What if he/she is assassinated? Or there are rival gangs? Or a drought? Or floods? Or EMP? Or a virus? Or....or....or....I think the point is made.
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At one point in my life I was studying Chaos Theory. One element of CT is known as "sensitive dependence on initial conditions." It means just a very tiny variation at the outset can have outsize consequences as that variation works through the system. It's where the idea of the "butterfly effect" comes from, the notion that a butterfly flapping its wings in China can, as the disturbance works its way through the system, cause a storm a month or two later in North America.
Once I realized Chaos Theory was telling me how to prepare, it was obvious what I should do: prepare capabilities, do not scenario plan. Oh, if there's a high probability of a specific event, like a hurricane, prep for that, but otherwise? Capabilities. It became crystal clear that I cannot predict what's going to happen--so I'd better be ready for...as much as I can, and to do that I need the big six to start.