The people are migrate are the members of the lower class who are exiled by law or economics or racism.
Read Albion's Seed -- the Borderers/Scotch-Irish were poor and exiled, following the model you describe, but the Cavaliers were both downwardly-mobile and eager to create ideological utopias, and the Puritans and Quakers were just looking for places to build utopia -- they were doing well enough economically back in England.