When did columbis discover America?

Answer 1

Columbus purchased maps to guide him to the America's from Portugeuse map makers indicating a prior knowledge of the continent by Europeans. The Vikings had already established settlement in what is nor Canada. The Chinese had explored the western coast of the continent.

Aside from this the continents of North and South America were already home to several viable civilizations and cultures all of which would have argued that, as they were there already, Columbus didn't need to "discover" them.