That public policy affects organizational behaviors is well accepted, but less explored is how these effects may depend on other external environmental factors. We investigate how policy is a necessary, but not sufficient, condition to understand the growth of commercial banking in the United States, 1896-1978. We highlight a trade-off for banks between centralized and dispersed growth strategies and show that which strategy prevails depends on how policy enabling branching interacts with technological, economic, and cultural environments. Our findings contribute to understanding the contingent effects of policy on organizations and on the growth of large corporations in the twentieth century.