The African slaves who were forced to fill this labor role in the American colonies were brought to North America on crowded and dangerous slave ships along the previously mentioned Middle Passage portion of the trans-Atlantic trade routes. The slaves were originally captured through the African slave trade within the African continent and then brought to the West African coast for barter with European slavers. Rum, cloth, weapons, and other manufactured goods from Europe were traded for Africans. Between three and four hundred slaves were packed into cargo holds of slave ships bound for North America. Sickness, fear, and brutality was the common experience for slaves on the Middle Passage. About two of every ten slaves died during the Middle Passage.

Prior to the cotton gin, slavery was nearly dead in the Upper South, awaiting its final benediction by state legislatures, and was dying a slow death in the Lower South. The cotton gin and westward expansion revived slavery. Eli Whitney invented the cotton gin in 1793. It is a machine that rapidly removes cotton plant seeds from the valuable cotton fiber used to make thread and fabric. By producing more cotton in a day than any person could clean by hand, the gin reduced the cost of processing cotton and greatly raised the profit from growing it. To further cut costs and raise profits, unskilled slaves were often put to work running the cotton gins in southern states.

Party politics were also affected by slavery. The two-party political system re-emerged in the early 1830s with the birth of the Whig Party. The party was short-lived as the issue of slavery fatally split the party by the end of the 1850s. New parties that were far more vocal on abolition, such as the Liberty Party and the Free-Soil Party, formed in the 1850s. These parties caused great fear among southerners who felt increasingly besieged, but by 1860 nearly all of these minor parties had self-destructed.

Henry Clay, a leading Congressman from Kentucky, is credited with putting together a compromise that resolved the issue. A key component of his plan hinged on the fact that Maine had also petitioned the Senate for admission to the Union. Maine had previously been part of Massachusetts and was slated to become a separate state. Clay’s Missouri Compromise included the following provisions. First, Maine would enter as a free state and Missouri would enter as a slave state, thus preserving the balance in the Senate. Second, the rest of the Louisiana Territory would be subject to a geographic division at the 36’30’’ line of latitude (Missouri’s southern border). Slavery would be prohibited north of the line. Slavery would remain untouched south of the line.

The abolition campaign included both men and women; Northerners and some Southerners. For the first time, Blacks began to play a significant role in the movement. Instead of a gradualist approach, the new abolitionists advocated for immediate emancipation without compensation for slave owners. Abolition became a divisive issue as the southern states reacted against growing hostility in the North toward slavery.

The United States, under the leadership of President James K. Polk, took Texas into the Union in 1845. As a result, war broke out between the United States and Mexico over differing frontier claims in Texas. The war proved to be swift and decisive as Mexico lost not only their land claim in Texas, but also all of California and New Mexico to the United States. The victory in the Mexican War soon pitted the North and South against one another as the United States wrestled with the slavery issue in the newly acquired lands. Sectionalism became even more bitter and the United States was quickly headed down a path towards Civil War.

The provisions of the compromise included:
1. The state of New Mexico would be established by carving its borders from the state of Texas.
2. New Mexico's voters would determine whether the state would permit or prohibit slavery.
3. California would be admitted as a free state.
4. All citizens of the United States, regardless of region, would be required to apprehend runaway slaves and return them to their owners. Those who failed to do so would be fined or imprisoned.
5. The slave trade would be abolished in the District of Columbia, but the practice of slavery would be allowed to continue there.

Despite the Compromise of 1850's passage, sectional tension over slavery was eased for only a short time.

The passage of the Kansas-Nebraska Act had several effects. First, the law virtually repealed the Missouri Compromise of 1820 and the Compromise of 1850. Settlers in all new territories would have the right to decide for themselves whether their new home would be a free or slave state. The second effect was that pro- and antislavery groups both hurried into Kansas in an attempt to create voting majorities there. Antislavery abolitionists came from eastern states; proslavery settlers came mainly from neighboring Missouri. Violence between the two sides created warlike conditions that led to the territory being referred to as "Bleeding Kansas." The third effect of the Kansas-Nebraska Act was that it split existing political parties into regional factions and gave rise to the new Republican Party. The common cause that attracted supporters to the Republican Party was opposition to slavery.

The Dred Scott decision gave slavery the protection of the United States Constitution. In essence, nothing short of a constitutional amendment could end slavery - an event not likely to occur. Proslavery Americans welcomed the Court's ruling as proof they had been right during their long struggle against abolitionists. In contrast, abolitionists convinced many state legislatures to declare the Dred Scott decision not binding within their state borders. The new Republican Party said that if its candidate were elected President in 1860, he would appoint a new Supreme Court that would reverse the Dred Scott ruling.

At first, many Northerners and Southerners were horrified by Brown's actions. Eventually, many Northerners came to respect what Brown had done, viewing him as a martyr for the abolitionist movement. Southerners were angered. Many in the South viewed Brown as a terrorist killer, a man that sought to incite a slave rebellion that would have led to the slaughter of hundreds of men, women, and children. Vocal Northern support of Brown's actions did little to calm an anxious South. Invoking the specter of the Nat Turner Rebellion nearly 20 years earlier, southern states began to strengthen and train their state militias. A war between the North and the South was becoming a real possibility.

Upon Lincoln's election, South Carolina voted to secede (separate from) the United States. Mississippi, Florida, Alabama, Georgia, Louisiana, and then Texas followed South Carolina in their break from the United States. These Lower South states were the original seven members of the Confederate States of America. Virginia, Arkansas, Tennessee, and North Carolina also joined the Confederacy. All of the events of the 1850s contributed to the outbreak of Civil War, but it was the election of Lincoln that triggered its actual beginning.