http://mytechnologyworld9.blogspot.in/2012/06/huge-ancient-civilizations-collapse.html
Or could they have gotten as politically fucked up with the wealth in too few hands like the current world climate?
It's all speculation, and we won't know the truth until we get to the Akashic Library, but I wonder if my idea isn't more realistic, not that probably half who have read this don't think the same.
Of course this set of comments is supposed to be read AFTER the link post, but hey. A lot of my commentary is like that.