One interesting thing to note about civilizations is that they have a nasty habit of collapsing. Many of them have come to their ends for similar reasons, and often the process of collapse has begun within only years of their reaching their maxima of geographical extent, military power, and accumulated wealth.
Clive Ponting, in his marvelous book A Green History of the World, offers a familiar explanation: ancient societies typically drew down their resource base and destroyed their habitat. They cut too many trees, exhausted their topsoil, emptied their wells.
Anyone interesting in learning more about this phenomenon, in order to get involved with the the coming economic and climatic challenges, could well take a look at Easter Island. http://www.eco-action.org/dt/eisland.html.
Civilisations follow the same pattern as animals when they crash. Take a look at what happened when a herd of reindeer were put on an island…