Yesterday, I was listening to this podcast over at Dan Carlin's "Hardcore History" site - I like his podcast quite a bit, and the topic yesterday - the Bronze Age Collapse - was fascinating. You can get some information on it here, at Wikipedia - but the problem is, we're talking about an era beginning around 1300 bc - so as you might expect, records are sketchy.
I don't know why I find systemic collapses so interesting, but I do. I really liked "The Fall of Rome and the end of Civilization", for instance - and while we know more about the fall of the western empire, historians still argue over what went wrong, why it went wrong, and why it got so bad (and even over whether it got so bad).
One thing seems to stand out in these kinds of collapses - before-hand, you had a world with a working system of international/long distance trade - which brought a fairly high level of specialization. Afterwards, you had a loss of connectivity, and - without local access to the kinds of specialized knowledge they had become dependent on, people fell backwards - sometimes very far backwards.
That makes me consider the modern world - just in time manufacturing, international trade that ties most of the world together, extremely high levels of specialization. The modern world is a fragile thing, and we sit just as much on the edge as the citizens of 4th century Rome did, or the citizens of 1300 bc Anatolia. As catastrophic as WWI and WWII were, they were like small hiccups compared to a systemic collapse. Something to think about, I guess.