Why did Native Americans migrate to North America?

The Early People crossed the land bridge(called Beringia because when it melted it became known as the Bering Strait) from Asia to North America thousands of years ago because the mammoths migrated there and if the mammoths left and the Early People didn't they wouldn't have food to eat. They would need some meat other than all vegetables. If they wouldn't have followed the mammoths, the mammoths would still be alive today walking our streets and destroying everything in its path. Also we probably wouldn't be in America if they didn't.