During the Ice Age, scientists believe people first came to the Americas from Asia by walking across a natural land bridge called Beringia. Others may have sailed from Europe. They were called hunters-gatherers. By 10,000 BC, glaciers melted, oceans rose, and land bridges disappeared. As early as 7,000 BC, scientists believe farming began.

Farming allowed the Olmec culture to grow in specific areas, such as government, education, religion, and architecture. The Olmec were one of the first groups to develop its own civilization in the Americas. The Maya were an early civilization in southern Mexico and Guatemala. For unknown reasons, the Maya left their cities and pyramids behind.

The Adena, one of the first groups of Mound Builders, were known for the large mounds they built to bury their dead. They also built mounds for religious reasons. In later years, the Hopewell settled in the Ohio River area where the Adena had been situated and continued the tradition.

Later still, a third group, the Cahokia, lived along the Mississippi. In the Southwest, Anasazi culture flourished from about AD 200 to 1300. They lived in cliff homes on the sides of canyons and farmed the desert using irrigation.