The first Americans crossed into North America from Asia over 30,000 years ago via a land bridge that connected Siberia to Alaska during an ice age. As the climate warmed, sea levels rose and the bridge disappeared under water. These early peoples adapted to different environments across North America by developing diverse cultures and ways of life, such as building shelters from local natural materials and hunting or gathering local food sources. However, they also shared some common beliefs like respecting nature and not owning land. Over time, distinct cultural regions developed across North America based on local environments and resources.