Don't Mess With Earth

In this alternate history novel..... humans discover that two groups of aliens have been manipulating human history since the pre-historic days. One group does this by posing as historical figures such as King Arthur, Galileo, Amelia Earhart, among others. The other group causes all sorts of historical anomalies such as the Salem Witch Trials and the disappearance of the Roanoke colonists.

Centuries later, when the humans from the country called the United States get a chance to study the technology of a downed alien ship in Roswell, they decide to do something about both groups of aliens. Once the scientists of Earth start reverse engineering the downed spacecraft, President Truman issues an executive order that will forever change Earth history.