In the histories of both the United State of America and Africa, migration of labour constitutes an important chapter. It is generally associated with the processes of change that entailed economic and social transformations. These transformations were observable on the part of both th~'origins and the destinations of the migrants. Labour migration on a significant scale meant a far-reaching disruption of economic and social life on the part not only of the individual migrants but of whole communities. Such a phenomenon can only be explained in terms of either sudden social upheavals or, more often, fundamental structural changes in society: