The Constitution had prohibited Congress from interfering in the transatlantic slave trade until 1808. On January 1, 1808, the Act to Prohibit the Importation of Slaves took effect. However, this did not abolish slavery; it merely dealt with importation of slaves. Slavery continued to be a contentious issue, as the United States tried to maintain a balance of slave states and free states so that neither side would have the upper hand in Congress.

In the North, abolitionists pressed for the end of slavery. Many argued both for religious and ethical reasons that the inhumanity of slavery had to be ended; Harriet Beecher Stowe’s novel, Uncle Tom’s Cabin (1852), describing the cruelty of the treatment of slaves engaged even more Americans in the urgent debate.

In the South, however, slavery was seen as an issue of states’ rights. And, some Southerners believed that if a Federal law was disputed by a state, that state could simply ignore or nullify it. (This led to the Nullification Crisis of 1832 in which South Carolina threatened to secede if a particular federal law was enforced. This view of the great power of individual states and the limited power of the federal government set the stage for the conflict over states’ rights and federal power in the matter of slavery.)

Furthermore, slaves were individual property and were extremely valuable to their owners. Also, the plantation economy of the southern states could not exist without the labor of slaves. In the North, the economy was more industrialized, and a flood of immigrants helped supply inexpensive labor for the factories. As the United States laid claim to more and more territory in North America, the problem of the extension of slavery into those territories became more pressing.

As of 1820, the Missouri Compromise had allowed Missouri to enter the US as a slave state (balanced by Maine as a free state), and established the “Mason-Dixon line” as the boundary between slave and free states. In the Compromise of 1850, California was allowed to become a state, entering the US as a free state, without a corresponding slave state being admitted.

However, a strict Fugitive Slave Act was established to assist Southerners, some of whose slaves were escaping to the North, where they were often sheltered by abolitionists. In another divergence from the strict one slave/one free state system of creating new states, the Kansas-Nebraska Act (1854) allowed Kansas and Nebraska to enter the US as either free or slave, based on a popular vote by their populations.

In 1858, Stephen Douglas (Senator from Illinois) and Abraham Lincoln riveted the attention of the nation with a series of debates on the subject of slavery. Douglas maintained slavery would eventually go away on its own, while Lincoln insisted it would require a change to the law to make this happen. The Republican Party, which was strongly opposed to slavery, chose Lincoln as its candidate in the election of 1860. Lincoln won a majority of the electoral college vote, although he lost the popular vote.

Even before Lincoln took office in 1860, the southern states began to secede. Eventually, eleven states seceded and formed the Confederate States of America. The Civil War (1861-1865) pitted two different ideologies and economies against one another. For the North, the goal was to force the Southern states to surrender. Their plan for doing this was nicknamed the “Anaconda Plan”; it involved encircling the South, blockading its ports, preventing it from exporting its cotton to Europe and from importing the manufactured goods that it could not produce itself.

The Southern plan was to outlast the North until their will to fight decreased and they were exhausted. What the South lacked in manufacturing, it made up for in good generals. Robert E. Lee and “Stonewall” Jackson were two of the South’s great generals. In the North, it took some time to find leaders who could effectively stand up to Southern generals. Ulysses Grant and William T. Sherman were two great generals of the North who ultimately helped lead the North to victory.

In 1863, as the war hung in the balance, Abraham Lincoln issued the Emancipation Proclamation, declaring that all slaves in the Confederacy were free. This did not end slavery, as some slave states were fighting on the side of the North. But, it did encourage Southern slaves to escape to the North. Some of these slaves joined the Union army, and by the war’s end, about 10% of the Union army was African American.

When the South surrendered at Appomattox in 1865, the problem remained how to re-integrate the southern states of the Confederacy into the Union of the United States. This process was called “Reconstruction” and it lasted from the end of the war until 1877. The Southern states rapidly demonstrated that they had no real intent to change how African Americans were treated in their territories. Thus, the Federal government divided the South into five military districts and forced the southern states to ratify the 13th, 14th, and 15th amendments which abolished slavery and guaranteed civil rights and voting rights to African Americans. Some southern states elected their first African American representatives to Congress. Efforts were also made to restore the South economically and to support former slaves.

However, as the process dragged on, the energy behind Reconstruction ebbed. In 1876, the Presidential election resulted in an electoral college nightmare; it was clear that the Republican, Rutherford B. Hayes, had not won the popular vote, and 20 electoral votes were disputed. In the end, the southern states agreed to give all 20 electoral votes to Hayes if the government ended Reconstruction. After the end of Federal pressure on the South, Southern states enacted segregationist “Jim Crow” laws that left African Americans in the South with virtually no political, economic, or social power.