Slavery was a central bulwark of the economy of the southern United States in the nineteenth century. While the North developed a wide range of industries and was economically diversified, the South attained vast wealth through its plantations, where owners practiced large-scale agriculture, growing such crops as tobacco, rice, sugar, and cotton using slave labor. Northern industries grew by milling the cotton raised in the South as well as by developing a wide range of manufacturing. Northern farms tended to be smaller and relied on family and hired labor.

Westward expansion and the growth of the territory of the United States was in part fueled by the search for new land for plantations. Small planters or even poor whites were psychologically enmeshed in the system of slavery because no matter how poor they were, they could feel superior to black slaves and have the hope of becoming wealthy planters themselves.

Slavery also made the United States more cosmopolitan, with a substantial African population who brought with them the roots of cultural hallmarks like jazz and blues music. But slavery also resulted in a legacy of racism, discrimination, and economic inequality which still endures. Segregation and inequality were the social and economic consequences of slavery.

An obvious consequence of slavery being accepted in the South but not the North was the Civil War, but there were also more subtle cultural divergences and antipathies.

Slavery had an overwhelming impact on the economy, politics, and society of the United States during the first sixty years of the nineteenth century. The most important effect was to divide American political culture into two increasingly irreconcilable factions until the differences exploded into a civil war.

While the United States remained an agrarian country during this period, the vast majority of the industrial development, or building of factories to turn raw materials into finished goods, took place in the north. Because of slavery, the southern states could base their wealth on growing and supplying raw materials, primarily cotton, which was then exported to England to be turned into cloth in the British mills. The region's economic dependence on slavery made it difficult for the south to abolish the institution because the plantations could not turn a profit without both a reliable labor supply (slaves cannot quit) and the almost nonexistent cost of a captive work force. However, at the start of the Civil War, the south was at a huge industrial disadvantage and knew it. It had no base for manufacturing weapons. It hoped that its superior military leadership and possibly the support of England, which depended on southern cotton supplies to keep its textile factories running, would lead to a quick victory. 

Politically, slavery polarized people to the point it paralyzed the country, dominating everything from western expansion (would new states be free or slave?) to Supreme Court decisions. The publication of Harriet Beecher Stowe's Uncle Tom's Cabin led to a political firestorm, with groups opposing slavery demanding its immediate end, while slavery supporters increasingly demanded that it not just be tolerated as a necessary evil, but approved as a social good. The demand that one be either pro or con on slavery tore the country apart.

Socially, the south developed a hierarchical society based on race that was agrarian and atavistic while the north increasingly embraced industrialism, equalitarianism, and progress. The south celebrated the leisurely life of the southern aristocrat and his military prowess, while the north appreciated hard work and business ability. The increasing revulsion of many northerners at the social evil of one person owning another, coupled with the south's increasingly entrenched defensiveness of an untenable and morally indefensible social institution, ripped the country apart. Slavery was not a situation in which one could have just a lukewarm opinion, and, eventually, a war was required to resolve the conflict.

Economically, slavery was at the heart of American expansion during the first half of the nineteenth century. After Eli Whitney developed the cotton gin, plantation slavery boomed. Southern planters and would-be planters looked westward for new lands, and the internal slave trade from the Upper South supplied hundreds of thousands of slaves to fertile cotton lands in Alabama, Mississippi, Louisiana and Texas. Despite a number of financial panics that caused prices to plunge in the short term, the overall trend for cotton prices was a rapid increase, as was the price of the slaves that worked to harvest the crop. By the time of the Civil War, cotton made up the vast majority of total US exports. All of this was based on chattel slavery.

In terms of society, slavery at first gave whites an opportunity to invest capital in a form of labor that could not only bring them riches, but could also allow them some degree of social respect. Slavery was the key to white democracy in the South, at least until the late midcentury, when rising prices meant that a decreasing percentage of white society had access to slaves. Indeed, by the time the war broke out, some southerners were beginning to argue that slavery depressed wages and limited economic opportunities for whites. 

Politically, the dispute over the expansion of slavery into the western territories, which was essentially about the degree to which white slaveholding southerners could use their power to ensure protection for the institution, tore the Union apart. Rising abolitionist (or anti-slavery, which was not the same thing) sentiment in the North caused many Northern politicians to view Southern actions as increasingly less tolerable. As almost every one of the secession ordinances for the Lower South states said explicitly, they left the Union to protect the institution of slavery, which they saw as being under siege from the North.