Scientists believe that there are 2 theories one consists of which the native Americans followed animals in Asia which led them following them all the way to Alaska on land by crossing a land bridge. The second theory consists of the natives following animals as well but this time they traveled on boat they went across the Arctic ocean with traveling on boat and ended in the Americas after a while.
The scientists believe that the first Americans came to North america by crossing the Arctic sea.
There is a difference between theory 1 and 2 fro example theory 1 is by land and theory 2 is by sea.
Even though both theories don't believe the native Americans traveled by land or sea the scientists believed once the natives came to america they spread around the country and lived in different places which made them have their own cultures.