It is generally believed that the Americas were first discovered by the Norse, I think it was Lief Erikson or something like that. They sailed from the tip of greenland, and found a new world where everything was perfect except for one thing: even the norse with their spears and arrows were beaten back by the natives. Rumors of this fabled new land reached Europe, where Columbus heard them and decided to see if they were true or not. He sold his idea to the royalty by claiming he wanted to see if there was a faster route to the east Indies. When he actually did hit the west indies, he thought he had hit the east Indies, but later voyages showed that he had indeed reached a new continent, thus proving that there was a new world. It took the Europeans with their guns and huge armies to overtake the new world from the Native Americans. The Americas were named after some other dude, can't remember how his name was spelled, Americus or something like that. Some ruins of buildings that are distinctly Norse in appearance have been found along the east coast of the United states.
Don't quote me on any of this, I got it all from reading about the travels of the norse, the Spanish conquest of the the Central American Indians, and a PBS special I saw about the norse ruins. I may have some of it a little mixed up, but you get the general idea.