Why do you think early peoples in the Americas immigrate south?
More farmland and areas to- well, farm:) The reason of that is that there are better resources down there and areas for their crops ro grow.
One of the main reasons people moved south was because of the weather. The higher up north you were, the colder it was. But the more south you went, like towards the south pole, it would get cold. So people tended to move south, near the equator. Hope that helped :)