Strong AI displaces humans as the dominant force on the planet.
A breakthrough is made the objective study of meditation, which makes triggering enlightenment much easier. Millions of people become enlightened.
Narrow AI solves protein folding, Atomically Precise Manufacturing (nanotech) becomes possible and affordable. (Post scarcity?)
The existing political order collapses.
The global economy collapses, supply chains break down. (Is this a thing that could happen?)
Civilization abruptly collapses.
Nuclear war between two or more nuclear powers.
A major terrorist attack pushes the US into heretofore unprecedented levels of surveillance and law-enforcement.
Sufficient progress in made on human health extension that many powerful people anticipate being within range of longevity escape velocity.
Genetic engineering (of one type or another) gives rise to a generation that includes a large number of people who are much smarter than the historical human distribution.
Significant rapid global climate change.