Mayans
Only they didn't say it ENDED, per se... but that the world is overturned, and a new order emerges.
The Aztec calender "end" famously coincided with the arrival of Cortez... a fact he used to his advantage.
Also, the demise of the city of Copan also coincided with Mayan calendar end period.
But with both of these historians cite the effect of self fullfilling prophesy... An army fully believing in the FATE of their destruction is unlikely to fight very effectively.
A populace convinced that their culture shall fall is susceptible to someone organizing an attack at that specific time.
And as we have leanred from the Rapture Right in the past 8 years...
Folks who BELIEVE the rapture is right around the bend do not PLAN for a raptureless future...
Economies and cultures can crash from nothing more than the belief that a crash is inevitable.
But the folks making this movie... I am sure they have residual and merchandising deals that have contract terms running well beyond 2012.
The apocalytics can always make a good buck BANKING on the apocalyse not occuring.