In the spring of 1860, Henry C. Carey, the Philadelphia political economist and apostle of protectionism, offered a revision of his doctrine in hope of saving the Union. For several years, in such writings as The Slave Trade, Domestic and Foreign (1853) and The North and the South (1854), he had argued that reimposition of high protective tariffs promised material prosperity for the free population and gradual emancipation of the slaves. With secession looming he enlarged the argument. In a series of letters to the Memphis Daily Enquirer, he explained how the original error of liberal trade beginning in 1833 had interacted with climate and migration to produce economic crises and sectional conflict. Political economy not only pointed to the right course, it showed why the course was blocked from view. Prosperity, gradual emancipation, and preservation of the union all depended on the inhabitants of the central "Mineral Zone," from Pennsylvania to Tennessee, first seeing the blockage and then uniting to correct the combined policy errors of the northern "Trading Zone" and the southern "Planting Zone." Carey's neglected "zone theory" shows the direction and ambitions of an important strain of American political economy in the immediate antebellum period. It also merits attention as an early example of economic theories of geography and institutions akin to those claiming attention today.