Scott v. Sandford (1857) for treating slaves as property. Stimulated by the philosophy of the Declaration of Independence, between 1777 and 1804 every Northern state provided for the immediate or gradual abolition of slavery. Most of the slaves who were emancipated by such legislation were household servants. No Southern state did so, and the enslaved population of the South continued to grow, peaking at almost four million in 1861. An abolitionist movement headed by such figures as William Lloyd Garrison grew in strength in the North, calling for the end of slavery nationwide and exacerbating tensions between North and South. The American Colonization Society, an alliance between abolitionists who felt the races should be kept separated and slaveholders who feared the presence of freed blacks would encourage slave rebellions, called for the emigration of both free blacks and slaves to Africa, where they would establish independent colonies. Its views were endorsed by politicians such as Henry Clay, who feared that the American abolitionist movement would provoke a civil war. Proposals to eliminate slavery by constitutional amendment were introduced by Representative Arthur Livermore in 1818 and by John Quincy Adams in 1839, but failed to gain significant traction. As the country continued to expand, the issue of slavery in its new territories became the dominant national issue. The Southern position was that slaves were property and therefore could be moved to the territories like all other forms of property. The 1820 Missouri Compromise provided for the admission of Missouri as a slave state and Maine as a free state, preserving the Senate's equality between the regions. In 1846, the Wilmot Proviso was introduced to a war appropriations bill to ban slavery in all territories acquired in the Mexican–American War; the Proviso repeatedly passed the House, but not the Senate. The Compromise of 1850 temporarily defused the issue by admitting California as a free state, instituting a stronger Fugitive Slave Act, banning the slave trade in Washington, D.C., and allowing New Mexico and Utah self-determination on the slavery issue. Despite the compromise, tensions between North and South continued to rise over the subsequent decade, inflamed by, amongst other things, the publication of the 1852 anti-slavery novel Uncle Tom's Cabin; fighting between pro-slavery and abolitionist forces in Kansas, beginning in 1854; the 1857 Dred Scott decision, which struck down provisions of the Compromise of 1850; abolitionist John Brown's 1859 attempt to start a