From the United States' foundation in 1776 through the 1850s, sectionalism gradually brought the country closer to Civil War. The issue of slavery dominated national politics, and both sides -- the North and the South -- rapidly hardened their opposition or support for the institution. Numerous compromises, including the Missouri Compromise and the Compromise of 1850, attempted to calm tensions, but ultimately failed when sectionalism exploded into war in 1861.
Missouri Compromise of 1820
Before 1819, there was a tight balance between slave and free states in the U.S. Senate. This calmed Southern fears by ensuring that pro-slavery elements could thwart Northern attempts to ban slavery; likewise, Northerners were happy that they could halt Southern attempts to expand slavery. In 1819, Missouri petitioned to join the Union, and both sides of the sectional crisis became concerned about whether Missouri would be a slave or a free state, because its admission as either would offset the fragile balance in Congress. A three-part compromise was thus struck: Missouri would join as a slave state, Maine would separate from Massachusetts as a free state, and the rest of the territory in the Louisiana Purchase would be divided, with the northern half closed to slavery and the southern half open to it.
Mexican War and the Compromise of 1850
The issue of western expansion continued to rouse sectional disputes, because it opened the door to more states in the union, and new states threatened to offset the national free-slave balance. This crisis reoccured in 1850, when California petitioned to join the Union as a free state. The pro-slavery South detested California's admission, because the state had a large population that would give anti-slavery elements in Congress significant numeric support. The Compromise of 1850 allowed California's admission as a free state, but also allowed other parts of the Mexican Cession region -- won during the Mexican-American War -- to decide on slavery on the basis of popular sovereignty. However, this left the slave-free balance unresolved, and enabled future states to ignite further sectional disputes.
Republicans and the Slave Power
By the mid-1850s, sectional tensions in Congress resulted in a new political party: the Republicans. A party of anti-slavery forces, the Republicans placed the national spotlight on the so-called "Slave Power." The party was almost exclusively composed of Northerners, who thought Southern forces in Congress had strangled national policies with the long-term goal of bringing slavery to the entire country. The Compromise of 1850, along with the Kansas-Nebraska Act and the Dred Scott Decision, seemed to support this thesis. Meanwhile, Southerners reacted to the Republicans with paranoia, believing the party was intent on eliminating slavery in the South. While some Republicans did indeed have this goal, most merely wanted to halt its expansion into the Western territories.
Election of 1860 and Secession
In 1860, the Republicans nominated Abraham Lincoln for the presidency. When Lincoln won -- the first Republican to win the White House -- Southerners reacted with panic. Despite Lincoln's stated commitment to halt slavery's expansion in the West, but maintain it where it already existed, Southerns believed he would ban slavery outright. Sectional jealousies came to a head, and South Carolina became the first state to secede by the end of 1860. Other Southern states, distrustful of the Northern section of the country, followed South Carolina's lead, and this rebellion resulted in the Civil War.
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