Over 12,000 years ago, groups of nomadic people began to emigrate across a land bridge that joined Asia to what is now Alaska. These were the ancestors of the tribes of North America, whose population was approximately 50 million by the time of the European arrival in the 15th century.
The societies and cultures of the many original North American tribes were diverse, and they can be divided into ten general culture areas whose groups share similar characteristics: Arctic, Subarctic, Northeast, Southeast, Plains, Southwest, Great Basin, California, Northwest Coast and Plateau.
Many tribes in these areas were small hunter-gatherer cultures, such as the Inuit, who followed the migration of seals and other animals for food. In other regions, however, there were large cities, such as Cahokia in modern-day Illinois, which had a population in the tens of thousands. Scholars estimate that there were up to 500 distinct languages spoken in North America prior to European arrival. While many tribes were nomadic hunter-gatherers, maize was an important dietary staple for others. The tribes that cultivated maize, such as the Hopi, were able to create food surpluses and settle into a more sedentary lifestyle, establishing greater concentrations of wealth, population and political power.