Many thousands of years ago, late in the Ice Age, humans journeyed across the Bering land bridge, from Asia into Alaska. Their descendants explored along the west coast of North America. As early as 1000 BC, they had covered nearly the entire continent. It is not known when the first people arrived in the Americas. Some archaeologists (scientists who study the remains of past human lives) believe it might have been about 12000 BC.

Over thousands of years, as they migrated across the continents, American Indians have developed a wide range of languages, customs, and civilizations. There are as many different tribal nations in the Americas as there are nations in Europe, Asia, or Africa, and there is as much variety among them.

Ten thousand years ago, when the Ice Age ended, changes in climate and increasing populations inspired some Native American tribes to experiment with growing different crops. Some became highly skilled farmers. As early as about 5500 BC, tribes in Mexico cultivated corn and squash. They raised turkeys, llamas, and guinea pigs for food and they hunted deer and bison. They regularly burned off patches of land to keep it in pasture, so the animals would come to graze. Many tribes on the coasts hunted sea mammals from boats and caught fish, using a variety of efficient methods.

After 2000 BC, some Native Americans developed states, each governing thousands of people. They established extensive trade routes across the continents. And they used cargo rafts and other boats to ship their goods from one trading point to another. In South America, llamas provided transportation on land.

From the present-day region of the mid-western United States to southern Peru in South America, centers of government were marked by enormous mounds of earth. Most of these mounds were flat on top, with palaces and temples built on them. Some were burial sites of honored leaders. American Indian cities were as big as the cities in Europe and Asia at that time. Their fine architecture is still greatly admired.

European invasions of the Americas began with Columbus's voyages to the "New World" in 1492. The Europeans brought diseases with them, including smallpox and measles. These unfamiliar diseases spread quickly among Native Americans. They wiped out the populations of many native cities.

The Europeans started colonizing the Americas in order to cultivate new farmlands and create new jobs for the growing populations of Europe. To do so, they often fought Native American tribal nations for the land. Several factors gave the Europeans the advantage in these conflicts. First, they had some immunities to their own diseases. Thus they were not as devastated by them as Native Americans were. Second, the Europeans had horses and guns, which overpowered the Native Americans' hand weapons and arrows in battle. Third, European settlements in the Americas grew at such a rate that the Europeans' descendants eventually outnumbered the native people.

Native American tribal nations resisted colonization, but eventually, many were forced to surrender their lands. In the regions of present-day southern Canada, the United States, and southern South America, survivors were gathered up and involuntarily moved to specific areas, called reservations. In Mexico, Central America, and northern South America, the native people were forced to live as peasants and laborers, under Spanish rule. In the last few decades, developments in transportation and earth-moving machinery have made it profitable for outsiders to colonize the tropical lowland forests. Now the way of life for those tribal nations, too, is threatened.

Today Native American populations across both continents are once again on the rise. Native American leaders are achieving greater political success in fighting for the rights of their peoples. In addition, recent widespread concern over human rights has prompted governments and others to respect Native American cultures and traditions when responding to their needs.