Slavery in the United States has played such a major role in US history that it has impacted many aspects of economics, culture, morality, and social progress.

By the time of the American Revolution, slavery was an integral aspect of the Southern colonies' economies. It was virtually impossible to get enough laborers for Southern plantation owners to be able to grow and harvest cash crops like tobacco, rice, indigo, and cotton, as the work was very difficult and would have been unprofitable if wages had to be paid. Many of our Founding Fathers, most notably George Washington and Thomas Jefferson, owned slaves and relied on slave labor for their wealth. During the Revolution itself, slaves were encouraged to fight against the British and were promised freedom.

Even so, many Americans abhorred the idea of slavery and wished the new republic would outlaw it. This, clearly, was a non-starter for Southerners who met to create the Constitution following victory in the Revolution. They agreed the Mason-Dixon line would be the demarcation between slave states in the South and free states in the North. This lasted until 1820, when the question of whether Missouri would be allowed to have slaves brought out a new debate. Southerners believed slavery to be a states' rights issue and lobbied hard for Missouri to be successfully admitted as a slave state, while Maine was admitted to the Union as a free state.

The next major battleground for slavery was Kansas in 1854, with pro- and anti-slavery activists flooding the territory and fighting to the point where it became known as "Bleeding Kansas." By this point in American history, cotton had become the dominant cash crop thanks to Eli Whitney's invention of the cotton gin: there were perhaps four million slaves in the South at this time. These slaves often lived brutal and short lives: abolitionist movements helped many escape, but the vast majority labored away in harsh conditions and under the threat of severe punishments.

The 1860 election of Abraham Lincoln was seen by Southerners as a catalyst to outlaw slavery and directly led to the Civil War. While the war was originally seen as a battle over both states' rights slavery, slavery became even more central to the war with the 1863 Emancipation Proclamation, which outlawed all slavery. While this was understandably unpopular with Southerners, it was also unpopular with many white Northerners, who did not want to think that they were fighting on behalf of blacks. Anti-draft riots in New York City broke out, and many blacks were lynched or burned alive.

The end of the Civil War and the adoption of the Thirteenth Amendment brought an end to slavery, but not an end to systematic racism. The Reconstruction-era South was plagued with white supremacist policies designed to keep blacks from voting, to keep blacks poor, and to keep them subservient to whites.

Slavery influenced the development of US society in the following ways:

1) The slaveholding aristocracy persisted throughout the nineteenth century. Southern society remained extremely hierarchical throughout this period. Southern slaveholders resented Northern democratic culture, which they considered vulgar. There was a cultural conflict between the growing Northern middle class and the Southern aristocracy.

2) An antagonistic conflict emerged between two alternative forms of economic development—that is, railroad building and the growth of an industrial economy protected from foreign competition by high import tariffs versus the development of an export-oriented economy based on the cheap production of cotton for the European textile industry. The South relied on slave labor to keep production costs low. The South resented the protectionism of the North; they wanted low import tariffs to keep the prices of foreign goods low.

3) The Southern states started the Confederacy, which led to the Civil War. They did this in order to preserve slavery. The Civil War resulted in the destruction of much of the Southern economy and society, but it succeeded in ending slavery.

4) Slavery led to the development of systematic racism. Most Southern slaveholders dehumanized African Americans, whom they treated primarily as a source of income. This paved the way for the post-Reconstruction Jim Crow laws and for the ongoing discrimination and racism that continue to plague American society today.