Quite a few of the past large political shifts were due to betrayal and spies, effectively also making months of work undone instantly. The current one was due

Quite a few of the past large political shifts were due to betrayal and spies, effectively also making months of work undone instantly. The current one was due to a bug or due to a player making a mistake. I don't think players cater all that much for the difference, and we'll likely never know which one it was.