Abstract
This paper employs the techniques of legal history to explore the relationship between the rise of big business and the size of the American market. It emphasizes law as a determinant of market size, and it analyzes judicial construction of the Constitution's commerce clause over time to delineate the role of integrated corporations in generating legal change. Specifically, the paper suggests that if the American market is defined as a free-trade unit, enlargement of the market was a result of, rather than a prerequisite for, the post-Civil War revolution in business organization.