On more optimistic... well, more Brave New World-type pessimistic days, I think that pockets of advanced idustrial civilisation will survive by the power of arms, while the majority of both those inside and outside won't see a disaster caused by the collective errors of the past, only on-going conflicts, and will be preoccupied with religions and insane ideologies.

On more apocalyptically pessimistic days, I think un-managed shortages will lead to a boil-down of current states, with them that of most large-scale economy, and seven billion people scrambling to survive will  in turn cause an ecological collapse, which in turn leads to famines and wars destroying even isolated pockets of civilisation.

_{*Lunatic*, n.
One whose delusions are out of fashion.}