At least 15,000 years ago, the ancestors of all the native peoples of the Western Hemisphere crossed the Bering Strait and wandered southward and eastward. Within a few thousand years the descendants of these Siberians, including the people Columbus called "Indians," had spread throughout the length and breadth of the Americas and built societies of tremendous complexity and accomplishment. Much of this history has remained hidden until recently because of both a lack of documentation and the political and racial biases of Americans who use the past to promote their own agendas. As the current generation of Americans rewrites its history, archaeologists have discovered new details that reveal a diversity of cultures, economies, and political systems that incorporated millions of people and hundreds of languages, all of which existed before the "contact" period with European explorers began in 1492.

A Continent of Cultures

As the first human inhabitants crossed the Bering Strait and moved onto the soil of North America, they found, during the Ice Age, a bountiful supply of big-game animals called megafauna. These animals supplied the earliest settlers with all their material needs. But as the Ice Age ended and ecosystems diversified as the glaciers receded, later generations had to adapt to the changing conditions. Adaptation formed the basis for the distinctive regional cultures that developed among the peoples in different parts of the Americas sometime between 10,000 and 2,500 years ago.

The most crucial adaptation for the development of North America occurred in Mesoamerica about 9,000 years ago, when the population began to domesticate plants, inciting an agricultural revolution in the Western Hemisphere. Because farming allowed these people to settle in one place, they began to build complex and large urban cultures. In these cities work became more specialized, which resulted in the development of palaces covered with art; marketplaces; schools; and suburbs for the common people. The Olmecs were the first city-builders in the Americas, but their accomplishments were outdone by the achievements of the Mayas, who developed cities with bridges, aqueducts, and observatories, as well as a sophisticated system of mathematics, a highly accurate calendar, and a written language.

These great Mesoamerican cultures did not survive; for reasons still undetermined by scholars, they disappeared by 950 C.E. Yet Mesoamerican influence is clearly visible in the peoples of the Southwest, where farming had spread by 1000 B.C.E. and where some architectural styles clearly resembled those of Mexico.

It is much more difficult to see the Mesoamerican influence among the peoples who ranged across the Eastern Woodlands of North America. Everywhere in this environment the inhabitants depended on a combination of fishing, gathering, and hunting, but around 2000 B.C.E. some groups in the Southeast began to cultivate gourds, pumpkins, and later maize. Most of the ancient Eastern Woodlands peoples did not adopt agriculture at all, and depended on hunting and gathering for their subsistence.

Among the cultures that developed in the Great Plains, the Great Basin, the Subarctic and Arctic regions, and in the Pacific Northwest, there was great cultural diversity. Great farming villages developed along the tree-lined streams and rivers of the Great Plains, but other people in this same region migrated with the seasons and relied for their survival almost entirely on hunting buffalo. In the Great Basin, while men did track and trap certain animals for food, the staples of their diet were seeds, nuts, and plants gathered by women.

The Inuit, people who lived in what is today the far north of Canada and Alaska, survived exclusively by hunting and fishing. Those people farther south in the Subarctic migrated from summer fishing camps to berry patches in the fall, to moose- and caribou-hunting grounds in winter.

In some important ways the early people of the Pacific Northwest were among the most culturally sophisticated in North America. The abundance of food and other natural resources in this region allowed for considerable leisure time to create works of art, plus an elaborate social and ceremonial life.

Innovations and Limitations

While these first Americans created a tremendously diverse group of cultures, they shared a common desire and ability to reshape their world. By experimenting with the resources around them, they created farming breakthroughs that have sustained peoples around the world. Plants domesticated by indigenous Americans, including corn, squash, potatoes, and beans, today account for three-fifths of the world's crops, and have revolutionized the world's diet for better and for worse. Native Americans also implemented more drastic changes in the landscape, from vast engineering projects in central Mexico and managed cultivation of the Amazon rainforest to re-routing of rivers and reshaping of forests in North America, all to enhance their agricultural production and further the building of their cities.

Yet certain natural realities constrained the ingenuity of these societies. Unlike Eurasia, which exists on an east-west axis, the Americas fall along a north-south axis, creating greater geographic and climatic diversity that made communication and technology transfer far more difficult than it was in the Old World. In addition, the scarcity of domesticated animals in the Americas meant that the population did not build immunities to disease comparable to those of their Eurasian counterparts, a distinction that would have disastrous consequences for Native Americans in the decades after European contact.

Crisis and Transformation

Great changes occurred in the cultures of the Americas during the three- to four-hundred years before the arrival of Europeans on these shores. Many well-developed and sophisticated cultures in America declined significantly or disappeared during this period of time. The explanations for their decline and/or disappearance are one of the past's greatest mysteries. Those inhabitants that remained struggled to construct new societies, with some of the most successful efforts occurring in the Caribbean and central Mexico. Both of these cultures were deeply stratified; in Mexico the Aztecs ruled over an empire that encompassed millions of people that they divided into classes of aristocrats, commoners, and even slaves.

The world that Columbus and other European explorers encountered after 1492 was astonishingly diverse. Somewhere between 9 and 14 million people lived in over 350 societies in North America and the Caribbean alone. In fact, their experiences were so varied that historians are still struggling to find stories big enough to encompass the lives of all the people living in this nation of nations.