@Olivier5,
I agree with you that some moments are truly pivotal, and that the collapse of the USSR waas indeed one of them. Moreover your insight about the accelerating flow of history that followed Fukuyama's rather pretentious and untimely declaration proved to be ironically accurate.
Complexity theory is something that has interested me since my grad school days working on complex numerical simulation of turbulent fluid flows. Led by a skeptical Meterorologist who produced some vivid demonstrations that it wouldn't work, the really smart guys in the field developed what became Chaos theory and the general proposition that the future state of non linear dynamic systems cannot be accurately predicted. That, of course had immediate consequences for Weather and Economic forecasting and many other established fields, and controversies that continue today.
Few things in life are more complex and full of contradictions than human behavior and the implications for the study of human history are profound. One interesting consequence of Chaos theory is that the gross properties of certain non linear complex systems do appear to present some quasi predictable features, even though the detailed "microstate" remains intractable. Your insight about the pivotal nature of events in 1990 got me thinking of others and the notion that this may be a model for productive analysis. Now that I think more about it this is merely an already commonplace notion among historians.
Anyway you got me thinking ....