The growth of public opposition to slavery represents one of the most momentous moral transformations in history. As late as 1750, no church condemned slave ownership or slave trading. Britain, Denmark, France, Holland, Portugal, and Spain all openly participated in the slave trade. Beginning with the Quakers in the late 1750s, however, organized opposition to slavery quickly grew. In 1787, the Northwest Ordinance barred slavery from the territories north of the Ohio River; by 1804, the nine states north of Delaware had freed slaves or adopted gradual emancipation plans.In Haiti in 1791, nearly a half million slaves emancipated themselves by insurrection and revolutionary struggle. In 1807, Britain and the United States outlawed the African slave trade.
Within the span of a century and a half, slavery, long regarded as an inevitable part of the social order, came to be seen as a violation of Christian morality and the natural, inalienable rights of man. The main impetus behind antislavery came from religion. New religious and humanitarian values contributed to a view of slavery as "the sum of all villainies," a satanic institution which gave rise to every imaginable sin: violence, despotism, racial prejudice, and sexual corruption. Initially, many opponents of slavery supported "colonization" -- the deportation of black Americans to Africa, the Caribbean, or Central America. But by the late 1820s, it was obvious that colonization was a wholly impractical solution to the problem of slavery. Each year the nation's slave population rose by 50,000, but in 1830, the American Colonization Society persuaded just 259 free blacks to migrate to Liberia, bringing the total number of blacks colonized in Africa to just 1,400.
In 1829, a 25-year-old white Bostonian named William Lloyd Garrison denounced colonization as a cruel hoax designed to promote the racial purity of the North while doing nothing to end slavery in the South. He demanded "immediate emancipation" of slaves without compensation to their owners. Within six years, 200 antislavery societies had sprouted up in the North, and had mounted a massive propaganda campaign against slavery. The growth of militant abolitionism provoked a harsh public reaction. Mobs led by "gentlemen of property and standing" attacked the homes and businesses of abolitionist merchants, destroyed abolitionist printing presses, attacked black neighborhoods, and murdered the Reverend Elijah P. Lovejoy, the editor of an abolitionist newspaper.
In the face of vicious attacks, the antislavery movement divided over questions of strategy and tactics. Radicals, led by Garrison, began to attack all forms of inequality and violence in American society, withdrew from churches that condoned slavery, demanded equal rights for women, and called for voluntary dissolution of the Union. Other abolitionists turned to politics as the most promising way to end slavery, helping to form the Liberty Party in 1840, the Free Soil party in 1848, and the Republican party in 1854. By the late 1850s, a growing number of northerners were convinced that slavery posed an intolerable threat to free labor and civil liberties. Many believed that an aggressive Slave Power had seized control of the federal government, incited revolution in Texas and war with Mexico, and was engaged in a systematic plan to extend slavery into the western territories.