History: American Civil War (1861-1865)

Northerners ranging from the abolitionist William Lloyd Garrison to the moderate Republican leader Lincoln emphasized Jefferson's declaration that all men are created equal. Lincoln mentioned this proposition many times, including his 1863 Gettysburg Address.
Almost all the inter-regional crises involved slavery, starting with debates on the three-fifths clause and a twenty-year extension of the African slave trade in the Constitutional Convention of 1787. The 1793 invention of the cotton gin by Eli Whitney increased by fiftyfold the quantity of cotton that could be processed in a day and greatly increased the demand for slave labor in the South. There was controversy over adding the slave state of Missouri to the Union that led to the Missouri Compromise of 1820. A gag rule prevented discussion in Congress of petitions for ending slavery from 1835–1844, while Manifest Destiny became an argument for gaining new territories, where slavery could expand. The acquisition of Texas as a slave state in 1845 along with territories won as a result of the Mexican–American War (1846–1848) resulted in the Compromise of 1850. The Wilmot Proviso was an attempt by Northern politicians to exclude slavery from the territories conquered from Mexico. The extremely popular antislavery novel Uncle Tom’s Cabin (1852) by Harriet Beecher Stowe greatly increased Northern opposition to the Fugitive Slave Law of 1850.
The 1854 Ostend Manifesto was an unsuccessful Southern attempt to annex Cuba as a slave state. The Second Party System broke down after passage of the Kansas-Nebraska Act in 1854, which replaced the Missouri Compromise ban on slavery with popular sovereignty, allowing the people of a territory to vote for or against slavery. The Bleeding Kansas controversy over the status of slavery in the Kansas Territory included massive vote fraud perpetrated by Missouri pro-slavery Border Ruffians. Vote fraud led pro-South Presidents Franklin Pierce and James Buchanan to attempt to admit Kansas as a slave state. Buchanan supported the pro-slavery Lecompton Constitution.
Violence over the status of slavery in Kansas erupted with the Wakarusa War, the Sacking of Lawrence, the caning of Republican Charles Sumner by the Southerner Preston Brooks, the Pottawatomie Massacre, the Battle of Black Jack, the Battle of Osawatomie and the Marais des Cygnes massacre. The 1857 Supreme Court Dred Scott decision allowed slavery in the territories even where the majority opposed slavery, including Kansas.