You've got it all wrong.
Around 900 AD: The Mayan Civilization disappears.
Reason: All the Mayans built towering time machines. The important people and many warriors were sent in.
The rest of the Mayans went to settle other civilizations.
What they planned: Their plan was to go into the future, where they expected there would be pyramids bigger than ones they had ever seen, and take over. There would be more land. As far as they knew, they would still be stronger than all the other civilizations around and be able to conquer anything that remained.
They chose the date 12/21/12.
What they didn't expect, and what will happen: The Mayans will come out of their time machine somewhere on the Yucatan peninsula. With their obsidian clubs, they'll surely be able to clobber a few tourists. Assuming they won't be killed right away, they'll make it to to capitol, where they'll try to attempt their raid and conquer.
What will happen after that?: It won't work. They'll be killed, and the secrets of time travel will be revealed to the world. The technology will only be shared with the allies of the United States. This will overall cause a war and nuclear bombs will be launched. The middle-east will be more chaos that it is. Everything will be destroyed.
Estimated end of the world?
Summer 2013
duh.
