Don't listen to MC's wikipedia post. Sandra Noble isn't noble at all. She's part of a Mayan advance team who's sole objective is to render us completely defenseless before the main fleet arrives. How are they accomplishing their goal? Well, do you see us preparing for a massive invasion?
Mission Accomplished.
However, if you read the Mayan Calendar backwards, it seems that the Mayans leave right after arriving. Some skeptics will tell you this is because we're just viewing events in the wrong order as a result of reading the calendar backwards. This is a lie. Anyone who tells you otherwise is part of the Mayan advance team.
On the off chance that I'm wrong about them retreating after traveling all that way to get back here, you should probably start arming yourselves. People wanted to know the real reason why Americans have guns. Now you know. We can't tell you where France is located, but we can defeat interstellar aliens with our rifles and pistols. Nothing will stop us from achieving victory over the alien scum.
You're welcome, world. You owe us. Again.
We actually have several Stargates in our country, all of which connect to the Mayan home world. We probably should have just sent a few nukes through them and hoped for the best, but that wouldn't have been action-packed as aliens destroying our cities while we rebel and eventually overcome evil, only to realize we had been infiltrated by a different kind of evil. That's right, Mr. Cheney. We know you're a 9' tall reptilian who uses holograms to makes yourself appear humanish. We'll take care of that when the time comes.
We also have two powerful allies. Long ago, right before the fall of the Roman Empire, they sent about a billion Praetorians into space. We call them Space Praetorians now. Because they're in space. Anyway, their goal was to conquer every planet in space in order to expand the glory of the empire. Amazingly enough, they succeeded. Mars was actually inhabited by cave dwelling civilizations. Where are they now? Space Praetorian slaves.
We also have the Hopi as our allies. I won't say anything about them because their prophecies have been right on the money so far, and I'm hoping they're wrong about the last one. But yeah, they have lasers so that helps.
In the mean time, board your windows, lock your door, fence your borders eat your children. We don't have time to care for the young.
Let's do this.