"The truth is out there somewhere!"
There are many alleged theories about aliens across the United States and the world. One theory is that the United States Federal Government may be allying with the aliens in order to keep their existence a secret. However, with thousands of people wanting to disclose on the government to prove existence of aliens such as Area 51, the government has done a poor job at trying to keep it a secret. Another theory says that some Earth people have come to conclude is that "we are aliens ourselves". Some believe that thousands of years ago, aliens used to live on the planet Mars. However the aliens noticed that the planet was starting to dry out, and decided to constructed a gigantic "mothership" to live once the planet was dried out.
They say that the aliens found Earth, the only (assumed) planet in the solar system capable of with staining living life. They say that the aliens left some of their offspring behind on Earth, and that the offspring evolved into humans that live on Earth. Some say the aliens want the U.S. Government to keep their existence a secret because the aliens plan to reveal themselves to the people of Earth one day. However, they are worried that the people of Earth are not ready for their advanced technology, but no one knows for sure.
There is another theory that aliens are simply future time-traveling humans, whose bodies have shaped and molded due to extensive space travel.
Conspiracy theories
Some believe that the grey aliens are nothing more than a figment of one's imagination, just like with any alien. Others believe that the US Government has an agreement with the aliens and that the aliens have asked the Government to keep their existence a secret by hiding their spacecraft and dead (and or alive) bodies at secret locations such as Area 51. The greys may believe that the human race is not yet ready for their advanced technology and want to wait to reveal themselves when the human race is prepared for their advanced civilization.
Countries, such as Russia, have created fabricated UFO sightings and alien bodies in attempts to throw the United States into panic. Because of the Russians' long history of rivalry with the United States, it would make perfect sense for them to create fabricated alien-related activity to compete with the US. However, there is no evidence that the grey aliens have ever been responsible for any Russian bombings and attacks on other countries including the United States. Even though the countries such as Germany and Russia are notable suspects for these fabrications, extraterrestrial enthusiasts believe that it may actually be the U.S. Government and the Central Intelligence Agency creating these false alien activity sprees. Although, it is unknown why or how.