In national politics, Southerners chiefly sought protection and enlargement of the interests represented by the cotton-slavery system. Expansion was considered a necessitybecause the wastefulness of cultivating a single crop, cotton, rapidly exhausted the soil, increasing the need for new fertile lands. Moreover, the South believed it needed new territory for additional slave states to offset the admission of new free states. Antislavery Northerners saw in the Southern view a conspiracy for proslavery aggrandizement, and in the 1830s their opposition became fierce.  

An earlier antislavery movement, an offshoot of the American Revolution, had won its last victory in 1808 when Congress abolished the slave trade with Africa. Thereafter, opposition was largely by the Quakers, who kept up a mild but ineffectual protest, while the cotton gin and westward expansion into the Mississippi delta region were creating an increasing demand for slaves.  

The abolitionist movement that emerged in the early 1830s was combative, uncompromising and insistent upon an immediate end to slavery. This approach found a leader in William Lloyd Garrison, a young man from Massachusetts, who combined the heroism of a martyr with the crusading zeal of a demagogue. On January 1, 1831, Garrison produced the first issue of his newspaper, The Liberator, which bore the announcement: "I shall strenuously contend for the immediate enfranchisement of our slave population.... On this subject I do not wish to think, or speak, or write with moderation.... I am in earnest -- I will not equivocate -- I will not excuse -- I will not retreat a single inch AND I WILL BE HEARD."  

Garrison's sensational methods awakened Northerners to the evil in an institution many had long come to regard as unchangeable. He sought to hold up to public gaze the most repulsive aspects of slavery and to castigate slave holders as torturers and traffickers in human life. He recognized no rights of the masters, acknowledged no compromise, tolerated no delay. Other abolitionists, unwilling to subscribe to his law-defying tactics, held that reform should be accomplished by legal and peaceful means. Garrison was joined by another powerful voice, that of Frederick Douglass, an escaped slave who galvanized Northern audiences as a spokesman for the Massachusetts Anti-Slavery Society, and later as the eloquent editor of the abolitionist weekly newspaper, Northern Star.  

One phase of the antislavery movement involved helping slaves escape to safe refuges in the North or over the border into Canada. Known as the "Underground Railroad," an elaborate network of secret routes was firmly established in the 1830s in all parts of the North, with its most successful operation being in the old Northwest Territory. In Ohio alone, it is estimated that from 1830 to 1860 no fewer than 40,000 fugitive slaves were helped to freedom. The number of local antislavery societies increased at such a rate that by 1840 there were about 2,000 with a membership of perhaps 200,000.  

Despite the efforts of active abolitionists to make slavery a question of conscience, most Northerners held themselves aloof from the antislavery movement or actively opposed it. In 1837, for example, a mob attacked and killed the antislavery editor Elijah P. Lovejoy in Alton, Illinois. But certain Southern actions allowed the abolitionists to link the slavery issue with the cause of civil liberties for whites. In 1835 an angry mob destroyed abolitionist literature in the Charleston, South Carolina, post office. When the postmaster stated he would not enforce delivery of abolitionist material, bitter debates ensued in Congress. In addition, abolitionists decided to flood Congress with petitions calling for a ban on slavery in the District of Columbia. In 1836 the House voted to table such petitions automatically, thus effectively killing them. Former President John Quincy Adams, elected to the House of Representatives in 1830, fought this so-called "gag rule" as a violation of the First Amendment. The House repealed the gag rule in 1844.