Who discovered the United States of America?

The United States of America was officially named on September 9, 1776. But people were living in the land that became the United States even before Christopher Columbus sailed there in 1492. Columbus is generally identified as the first European to set foot on mainland North America (in present-day Florida) in October 1492. However, native cultures developed independently on the vast expanse of the North American continent over the course of the previous 15,000 years (or even longer according to recent findings).