There is a theory that the North American Indians (so-called "Native Americans") crossed over from Asia by way of a land bridge that once existed in pre-historic times between the two continents - roughly along the lines of the Aleutian Island chain.
From where did early north Americans migrate?
Slavery
Case they war cool on their country
yes.
They migrate southwards in early fall, and winter from Mexico to Peru. Return north in April.
Walked across a land bridge.
The civil war they migrated because they where slaves for the south.
because the climate went warmer
Jim Crow was still very alive in the south and the North was about change and more equal opportunities.
By boat.
There are regions where irrigation systems would be particularly important for early North Americans. The great plains did well with irrigation.
Early Americans, or Native Americans, migrated from East Asia to North America and then from here into South America, where their people flourished for thousands of years.
The answer is Beringia.