In the United States, most abolitionists were Northerners. However, it is important to keep in mind that most Northerners were not abolitionists. Many Northerners were apathetic or ambivalent about the issue of slavery. While there were also many people who opposed the spread of slavery or wanted to gradually phase it out, the abolitionists wanted its total and immediate end.

The abolitionist movement began in the early 1830s. William Lloyd Garrison is often credited as being the founder of the American abolitionist movement. His weekly publication, The Liberator, galvanized strong anti-slavery sentiment across the free states. However, it was quickly banned in much of the South.

Many abolitionists formed organizations such as the American Anti-Slavery Society, the American Missionary Association, and the Liberty Party. Societies such as these lobbied politicians to bring about an immediate end to slavery. They also supported freed and escaped slaves through charitable programs. Black abolitionists also became prominent figures in the movement. Frederick Douglass, a former slave, became a major leader in the abolitionist movement.

In the years before the Civil War, abolitionists had a hugely disruptive effect on American society. Many saw them as agitators upsetting the delicate balance between pro-slavery and anti-slavery interests that had been maintained since the country's founding. There were frequent outbreaks of violence between abolitionists and pro-slavery groups. For instance, Kansas was settled by both parties. Fighting between slave owners and abolitionists became so intense that the foundational period of Kansas was referred to as "Bleeding Kansas". Abolitionists in the South were regularly attacked. Southerners feared that abolitionists would be the catalyst of a slave rebellion. In fact, their fears were nearly realized when the abolitionist John Brown seized an armory with the intent of arming slaves. All of this societal strife escalated tensions to the point that the Civil War became inevitable.