- Resource depletion. Humanity expands beyond a point resources are capable of supporting and we happen to have moral quandaries with killing off civilisation to restore balance. Chaos ensues. Earth is exhausted, unable to return to it's previous state and is currently capable of supporting about 5% of all humanity.
- Universal Corrosion. Rather than zombies another unstoppable virus targets earth and effectively destroys the fundamental materials we use to build things; causing chaos and panic worldwide and humanity basically kills itself in the process.
- Digital AI Uprising. Like robot uprising, except not physical robots but all our machines turning against us... Override our systems and throw our own nukes at us.
Prolly more. Maybe later.
- Succubi with aids.