Arabic came in later. The late 19th-century diffusionist geographers had looked at cultural diffusions, but they saw techniques moving and not people. Yet, people move too. Population movement is the most elementary kind of culture contact, because people move and take their culture with them. Broad population movements tell you about how things became the way they are, how human societies change through time.
Migration is one of the fundamental ways societies change through time.
United States popular culture sees the American experience as uniquely marked by migration. That is one of the many forms of American exceptionalism that some US historians have held. I don't think it is true that the US experience is so unique. In Australia they built a democracy but they didn't have the family farm or anything else that we thought made democracy here. Parts of what we learn in US history just do not make sense in the Australian context.