The exact nature of Civilization: Beyond Earth's "Great Mistake" has been the subject of much debate since being revealed as the game's cryptic backstory, and that ambiguity was absolutely deliberate, lead designers Will Miller and David McDonough said during a Firaxicon panel devoted to the catastrophe, a choice meant to reinforce the game's focus on the future, rather than distracting players with details about the past.
That hasn't stopped Miller and McDonough from having some fun imagining how an event like The Great Mistake might actually take place. In their mind, The Great Mistake had to fulfill certain requirements in order to prove disastrous enough to compel the world population to establish civilization on a new planet. It had to produce three kinds of upheaval -- territorial, population, and technological. They believe that nuclear war -- specifically, a dirty bomb detonating in a Chinese urban center -- would be the most efficient means of meeting these criteria.
Here is the chain of events as they imagine:
- Dirty bomb
- China blames Iran and blasts Iran and Afghanistan with a nuke.
- Pakistan attacks China
- China nukes Pakistan and North Korea
- This causes a refugee crisis, as populations are displaced globally.
- Climate change is accelerated, and the sea level rises.
- Governments become increasingly isolationist and turn inward to resolve devastation.
- It is not until four generations pass that humans begin to look elsewhere for Earth-like habitats.
Again: this is all hypothetical, and -- as Miller and McDonough stressed multiple times -- ABSOLUTELY NOT CANON (so don't go adding this information to the wikia.) The true nature of the "The Great Mistake" is entirely up to you -- so share your take on the globe-decimating disaster in the comments!