I find the idea of Kondratieff cycles interesting, but I'm a bit skeptical - what's the best reference on this?
I recently read The Coming Generational Storm by Kotlioff and Burns, and while it is focuses on the fiscal issues that will specifically hit the US due to demographic change, it touches on the general aging trend through the developed world. It seems to me that Europe is more vulnerable since if you don't feel like paying German taxes, you can leave, but it's not that easy for the US.
(As an aside, the book really drove home why government-financed retirement provision is pernicious and socially destructive - at least in my opinion.)