The joint analysis of interregional and interpersonal income disparities leads to a reformulation of regional development theory. A two-stage conceptual framework is proposed: firstly, the notion of region is redefined in terms of the two concepts of mode of production and social formation; secondly, the relationship between long swings in capital accumulation and unequal regional development are discussed. Two examples are then used to illustrate the theory: the spectacular rise of the South in the United States, and the continued unequal development between Québec and Ontario in Canada.