This paper traces the political and social tensions over slavery that culminated in the American Civil War. Beginning with the compromises embedded in the 1787 Constitutional Convention, it examines the Missouri Compromise of 1820, the Compromise of 1850, the Kansas-Nebraska Act, the Bleeding Kansas violence, and the Dred Scott Supreme Court decision. The paper explains how the election of Abraham Lincoln in 1860 prompted Southern secession under the compact theory, surveys the major military campaigns of the war, and concludes with the Union's preservation at Appomattox and the staggering human cost of the conflict.
Even at the Constitutional Convention of 1787, American leaders recognized a fundamental dividing line between states that permitted slavery and those that did not. Many attempts were made to defer the issue rather than resolve it: the Three-Fifths Compromise, the constitutional guarantee not to end the slave trade before 1808, and the banning of slavery in the Northwest Territories through the Northwest Ordinance. Northerners hoped the South would come to recognize slavery as economically inefficient and abandon it voluntarily. Southerners, for their part, hoped that an agrarian coalition with the West could prevent Northern commercial interests from dominating national policy — a hope that seemed realized when Thomas Jefferson won the presidency in 1800.
The economic reality, however, was that cotton prices were booming and Southern planters were highly profitable. At the same time, the view that slavery represented a form of barbarism was gaining ground internationally, and slaveholding societies found themselves increasingly isolated. Abolition had come to the Northern states shortly after the Revolution. Haiti abolished slavery and established an independent Black republic in 1804. Britain banned the African slave trade in 1808. In the years that followed, the Republic of Colombia, Venezuela, Ecuador, Panama, Mexico, Peru, Chile, and all other nations that had won independence from Spain outlawed slavery as well. By 1833, only three large nations still practiced slavery: Brazil, Cuba, and the United States.
In the meantime, the expansion of American democracy under Andrew Jackson extended voting rights to all white men, regardless of property ownership — while simultaneously stripping voting rights from women in states such as New Jersey and denying them entirely to Black men. These questions of political participation became critically important when Missouri applied for admission to the Union in 1818, igniting fierce conflict between pro-slavery and antislavery forces over whether the new state would permit slavery.
The Missouri Compromise of 1820 was an agreement between pro-slavery and antislavery factions to govern the expansion of slavery into the Western Territories. Missouri's first bid for statehood came before the House of Representatives in February 1819. Representative James Tallmadge of New York immediately introduced an amendment prohibiting the further importation of slaves into Missouri and requiring that all children born to enslaved people there be freed upon reaching the age of 21. The House adopted the amendment, but the Senate rejected it, and the effort stalled entirely.
The following year, a similar bill was taken up, and a comparable amendment introduced by Representative John Taylor of New York — requiring any new state constitution to include a provision for the abolition of slavery — was approved. The situation had grown more complicated by this point: Alabama had been admitted as a slave state, and Maine was seeking admission as a free state. The Senate proposed admitting both Maine and Missouri simultaneously, granting Missouri the right to draft its own constitution. Senator Jesse Thomas of Illinois then introduced the critical amendment that defined the compromise: slavery would be prohibited in all territory north of latitude 36°30´ — except within Missouri itself.
The matter was referred to a joint committee, ultimately producing two separate laws — one admitting Missouri and one establishing the 36°30´ line — both approved by President James Monroe in March 1820. One lasting consequence of the Missouri crisis was the transformation of American politics into a more firmly two-party system, with both parties consciously working to keep sectional issues from disrupting national governance. That uneasy arrangement held until the end of the Mexican-American War, which delivered vast new territories to the United States and forced Congress to confront the slavery question all over again.
The discovery of gold in California in 1848 triggered a massive migration to the territory. Mormon settlers had already established themselves in the Salt Lake Valley, in the northeastern portion of the Mexican Cession of 1848. Meanwhile, the slaveholding state of Texas claimed half of present-day New Mexico. These pressures compelled politicians to negotiate the Compromise of 1850. Under its terms, California was admitted as a free state; the remainder of the Mexican Cession was divided into the Utah and New Mexico territories to be organized under popular sovereignty; Texas received no territorial expansion; the slave trade was abolished in the District of Columbia; and a strengthened Fugitive Slave Act was enacted. Many observers felt the overall settlement leaned toward Northern preferences, though it included provisions intended to satisfy both sides.
In practice, the compromise satisfied neither. The Fugitive Slave Act outraged Northern antislavery opinion, while Southerners felt that California's admission as a free state tilted the balance of power permanently against them. The truce it produced would last only a few years before the next crisis broke it apart.
"Popular sovereignty, illegal voting, and frontier violence"
"Supreme Court ruling and Southern states leaving the Union"
"Military campaigns, Appomattox, and Union preservation"
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