The most famous secession movement was the case of the Southern states of the United States. Secession from the United States was declared in eleven states (and failed in two others); they joined together to form the Confederate States of America (CSA). The eleven states of the CSA, in order of secession, were: South Carolina (seceded December 20, 1860), Mississippi, Florida, Alabama, Georgia, Louisiana, Texas, Arkansas, North Carolina, Virginia, and Tennessee (seceded June 8, 1861). Secession was declared by its supporters in Missouri and Kentucky, but did not become effective as it was opposed by their pro-Union state governments. This secession movement brought about the American Civil War. The position of the Union was that the Confederacy was not a sovereign nation-- and never had been, but that "the Union" was always a single nation by intent of the states themselves, from 1776 onward-- and thus that a rebellion had been initiated by individuals. Historian Bruce Catton described President Abraham Lincoln's April 15, 1861, proclamation after the attack on Fort Sumter, which defined the Union's position on the hostitalities: After reciting the obvious fact that "combinations too powerful to be suppressed" by ordinary law courts and marshalls had taken charge of affairs in the seven secessionist states, it announced that the several states of the Union were called on to contribute 75,000 militia "...to suppress said combinations and to cause the laws to be duly executed." ... "And I hereby command the persons composing the combinations aforesaid to disperse, and retire peacefully to their respective abodes within twenty days from this date.