The first Americans migrated to North America over a land bridge that connected Siberia to Alaska around 30,000 years ago during an ice age. As the climate warmed, sea levels rose and the land bridge disappeared, leaving early Americans isolated in their new environments across North and South America. These groups developed diverse cultures and ways of life based on the varied natural resources of their regions, such as coastal communities relying on fishing or plains tribes following buffalo herds. However, most Native American cultures also shared some common beliefs, like respecting nature's spirits and only taking what was needed from the environment.