Christopher Columbus may have been the first European to sail across the Atlantic Ocean to the Gulf of Mexico, but he was not the first to discover the Americas. Human migration dates back to nearly 200,000 years ago. At approximately 15,000 years ago Humans crossed a land bridge called Beringia from Asia to Alaska. As a result, human migration and settlement occurred across both North America and South America 1,000's of years before the Nina, the Pinta, and the Santa Maria landed at Hispaniola in the Gulf of Mexico (Columbus). Humans chased game across the exposed land that is today's Bering Strait. Because the Earth was much cooler 15,000 years ago, an increased amount of seawater was frozen into the polar ice caps. The consequence was that areas of land were exposed that today are under water.
The first humans chased wild game across Beringia for survival. Eventually these humans migrated into the lower latitudes of Canada and into the present day United States. After several millennia, these humans had crossed Panama and spread across the South American continent. By the time of European contact humans had spread across all corners of the western hemisphere. Early on these humans were labeled "Indians," but today we refer to peoples with this ancestry as Native Americans.
Native Americans, as mentioned above, existed all across the Americas. In Canada and the United States there were hundreds, possibly thousands of differing tribes. These Native Americans carved out different ecological niches to survive. For example, some Native Americas relied on hunting buffalo across the plains; whereas others used agricultural techniques to sow corn. In addition, Native Americans that settled in present-day Mexico and the Andes Mountains of South America built cities that rivaled European cities. One example is the Aztec capital city of Tenochtitlan. The Inca, Maya, Pueblo, Kiowa, Iroquois, Cherokee, Pawnee, Yokut, Seminole, Eskimo, and many other tribes already inhabited the Americas for thousands of years prior to the voyage of Christopher Columbus.