In his lively and readable Special Providence: American Foreign Policy and How It Changed the World , Walter Russell Mead emphasizes early America’s dependence on foreign trade. A Congressman said in 1846 that Illinois needs “the market of the world” for its agricultural products, since “Ten counties of that State could supply all the home market.”

In short, “Access to foreign markets was a requirement for American farmers, in remote settlements,” and they knew it. For many politicians and thinkers of the period, therefore, “control of New Orleans and its port was essential not merely to national happiness but to unity. While Davy Crockett and Daniel Boone roamed the Appalachian wilds, informed opinion in the United States and abroad held that the Middle West would not remain in a federal union that could not provide its inhabitants with safe access to international markets. The volunteer backwoodsmen who followed Andrew Jackson to New Orleans knew why the city was fundamentally important to American prosperity and union, and they grasped the importance of the battle they fought there.”