This verse shows that after the days of Noah, the people stayed together. They had moved to other places together, probably due to the growth of their population. The new humanity had started at mount Ararat, but the Bible does not tell where they moved after that. All we know from these verses is that they migrated eastward and ended up in a plain of the land of Shinar. This pertains to the entire world population at that time. The “whole earth” (see Genesis 11:1) went to the land of Shinar.
2 And as people migrated from the east, they found a plain in the land of Shinar and settled there.