The End of the End of Civilization

The end of civilization, one of the big questions is why does it end? And it ends about 4000 years ago. So I hear we've got a mini quiz for you here. Which of these four has not been suggested as a reason for the end of the end of civilisation? Not been suggested, got it? Good. That just says this is Sanjay, the one horned buffalo. Oh, excellent. We're glad we cracked the case. The actual answer is meteor because I made that up. But what we do know is it's a slow process of decline or kind of a transition. All of the urban centers had reduced or been abandoned by the 1900s PC.