Step 1: Energy Crisis
As it turns out, major corporations have been lying to us. The oil and gas reserves turn out to be completely depleted by 2017, and all sales only came from allready mined deposits too keep up apearances. There is a massive push for alternative Energy, but it will still take years to actually build the required infrastructure. Huge swaths of the population are suddenly cut off from electricity.
Step 2: Economic Collapse
The lack of electricity and fossil fuels leads to a collapse of 90% of all Industry. The divide between poor and wealthy worsens massively, with the wealthy/powerfull maintaining highly protected conclaves that subsist on their own powergrids. Starvation sets in as international trade colapses. The first world is hit especially hard.
Step 3: Riots
Order in the streets has long since colapsed. The poor lead continous rebellions against the rich. The rich employ more and more drastic methods to controll the poor. 207
In addition the poor turn on each other in their bid for survival. Ideologies and Religions are forged as coping mechanisms against the daily struggle; These come in two flavors:
1. Repentists, who think we are being punished for our transgression, and aim to destroy all that remains of the old world in their quest for absolution.
2. Punishers, who think that we are all paying for the mistakes of the "Leading Elite", and aim to destroy all signs of the old "opressive" world order.
Books and heretics are burning in the streets, everyone enjoys the bonding experience. If you enjoy science or critical thought you help everyone stay warm, by feeding the bonfires.
Step 4: Apocalypse
Now that we ourselves have destroyed most anything that could helps us recover, an actual apocalypse sets in. Let's for example say, that the automatic reaction systems in our mutualy assured destruction protocols don't take kindly to neglect and laymans fiddling with them.
An atomic winter starts.
Step 5: Decay
What remains of society is made up off those few wealthy who persisted through the riots and their guards (read: private armies), everybody else lacked the resources, protection, or organisation. As the survivors are only made up of those that were allready willing to take any neccessary step to isolate themselve from the world, morality of the survivors is questionable even for these extreme conditions.
The remaining societies decay into military dictatorships. Education is kept low in order to make control of the population easy.
Isolation due to the post-apocalyptics effects keeps the genepool small, and along with the radiation, genetic and mental defects become common place.
After the isolation ends, the only thing that remains of mankind are inbred pseudo-humans. The only thing remaining of the past is the somewhat militaristic seeming clan structure of those that survived. 207