On December 20, 1860, a little more than a month after Republican Abraham Lincoln had been elected the 16th president, a convention met in Charleston and passed the first ordinance of secession by one of the United States, declaring, "We, the people of the State of South Carolina in convention assembled, do declare and ordain... that the Union now subsisting between South Carolina and other States, under the name of 'the United States of America, ' is hereby dissolved." That came two days after the failure of the Crittenden Compromise, a proposed Constitutional Amendment to reinstate the Missouri Compromise line and extend it to the Pacific failed.

President Buchanan supported the measure, but President-Elect Lincoln said he refused to allow the further expansion of slavery under any conditions. In January 1861, Mississippi, Florida, Alabama, Georgia, Louisiana and Kansas followed South Carolina's lead, and the Confederate States of America was formed on February 4 in Montgomery, Alabama, with former Secretary of War Jefferson Davis inaugurated as its President. A few weeks later Texas joined, and after Fort Sumter several more states would secede and join the Confederacy, most notably Virginia.

The election of Abraham Lincoln was the impetus for the secession of the South, but that was merely one of many events that led up to the formation of the Confederacy and the start of the Civil War. Sectional hostility over the issue of slavery had been bubbling for most of the 19th century, and violence had already broken out in places like Bleeding Kansas. Political issues like the Missouri Compromise, popular sovereignty, and the Fugitive Slave Act all added to the arguments.
The secession of the South was one of the seminal events in American history, but it also remains one of the most controversial. Over the last 160 years, the greatest debate over the Civil War has remained just what caused it, and as recently as April 2010, Virginia's governor declared April "Confederate History Month in Virginia," issuing a proclamation that made no mention of slavery. Facing an intense backlash, Virginia's governor first defended his proclamation by noting "there were any number of aspects to that conflict between the states." Days later, the governor apologized for the omission of slavery. In turn, the governor's backtracking was criticized by many Southerners, most prominently the Sons of Confederate Veterans, a large organization dedicated to commemorating the Confederates. The governor later declared that there would be no Confederate History Month in 2011.

Arguments over the war's causes are nothing new. Before the war had even ended, Confederate soldiers were asserting that they were fighting for states' rights. In the early 20th century, prominent historians such as Charles Beard theorized that the war was based on economic differences between the North and South. Although slavery had been the dominant political issue in the 50 years leading up to the Civil War, these historians began to assert that slavery was not necessarily a factor.