Although some Americans, including Southerners, had sought an end to slavery since the eighteenth century, modem abolitionism is usually dated from the early 1830s. Those years witnessed a religious revival that committed Christians to the extirpation of sin, the initial publication of William Lloyd Garrison's newspaper, The Liberator, Parliament's abolition of slavery in the British West Indies, and the formation of the American Antislavery Society. Attracting both black and white men and women of intense religious fervor who fumed at the apparent moral complacency of their fellow Americans, modem abolitionism was distinguished from preceding and other contemporarious antislavery groups in two ways. First, it rejected the gradual approach to emancipation represented by northern states' post-nati emancipation laws or programs to colonize free blacks in Africa in order to induce southern masters to manumit their slaves. Instead, it advocated the new doctrine of "immediatism" which theoretically meant the instant, root-and-branch, uncompensated abolition of slavery in the United States. In practice, however, "immediatism" meant organizing and agitating to convince Americans, especially Southerners, that slaveholding was so sinful that Americans must immediately begin its total eradication. Second, abolitionists also insisted that blacks were the equals of whites, that racism also required instant extirpation, and that freed slaves must be incorporated into American society as white's social and political equals. Arguably, indeed, while most Northerners rejected abolitionists' call for immediate emancipation because it could provoke southern disunion, it was their insistence on racial equality in the North, as well as the South, that generated white Northerners' vehement opposition to abolitionists and prevented the movement from encompassing more than a tiny minority of Northerners.

At least initially, abolitionists relied on moral suasion to persuade individual slaveholders to free their slaves rather than on the coercive power of government. In the mid-1830s, abolitionist societies attempted to flood the South with antislavery propaganda, sent through the mails, only to be blunted by southern state laws and local pressure that forced southern postmasters to destroy these materials rather than distribute them. Abolitionists, however, also petitioned Congress to abolish slavery or at least the slave trade in the District of Columbia. While the circulation of petitions for signatures in northern communities instilled a sense of actually doing something for the antislavery cause, especially among women, thereby facilitating recruitment of members for abolitionist societies, "Gag Rules" that suppressed debate on these petitions effectively stultified this campaign, even as they shifted the northern public's focus away from abolitionists' main goals — immediate abolition of slavery and racism — to the defense of whites' right of petition and freedom of speech.

By 1838, when membership in the local affiliates of the American Anti-Slavery Societies peaked at approximately 300,000 men and women, therefore, antislavery agitation had reached an apparent dead-end. Abolitionists then divided into rival organizations over the best way to revive the movement's momentum. Proponents of slavery's immediate abolition would persist into and beyond the Civil War, but by the late 1840s they would be displaced as the main voices of antislavery sentiment in the North by free-soil or anti-slavery extension political organizations which often advanced overtly racist reasons for stopping slavery's expansion that repudiated the racially egalitarian values of the 1830s abolitionists. Opposition to slavery's extension, not the abolitionist program of ending slavery everywhere, would be the chief platform of the Republican party that elected Lincoln president in 1860.