Civilisation is a fascinating topic but I haven't had a chance to look into it properly. Quigley, Chodorov and Russell have all done work and all three I have set to go when I can get to them. I also have Huntington which I did have a look at but I suspect he is a bit of a fake.

I'm not convinced about Toynbee. Sounds too ordered to me. Yes there would be some challenges encountered and conquered but there would also be challenges smaller and larger than goldilocks size, and also periods of no challenge. Unless he has shown that every civilisation in those other circumstances fell, his theory fails.