Following the election of Abraham Lincoln on an anti-slavery platform, the major slave-holding states declared their secession from the United States one after another. They formed the Confederate States of America (commonly called the Confederacy) under their own president Jefferson Davis. Below is a list of the 11 seceding states during the American Civil War, along with the date of secession and when they were readmitted.

NOTE: Four other slave states?Delaware, Maryland, Kentucky, and Missouri?remained in the Union. The latter two were actually represented on the Confederate flag, which, like the Stars and Stripes, featured a star for every state.

1. Date of readmission to representation in U.S. House of Representatives.

2. Second readmission date. First date was July 21, 1868, but the representatives were unseated March 5, 1869.

Although more than a century of states' rights debates have muddied the waters, the reasons for secession are actually quite clear. All eleven states declared slavery as one of the primary motivators for their secession; they believed that their livelihoods were tied up with the institution of slavery, and that they could no longer be part of a country that might force them to abandon slavery. The declarations of secession all contain similar messages. Of all of the many rights they felt the federal government might strip away from them, slavery was the biggest.

But, the situation is a bit more complicated in terms of why they finally seceded when they did.

Let's take the example of Georgia. The secessionists there wrote:

"The people of Georgia having dissolved their political connection with the Government of the United States of America, present to their confederates and the world the causes which have led to the separation. For the last ten years we have had numerous and serious causes of complaint against our non-slave-holding confederate States with reference to the subject of African slavery. They have endeavored to weaken our security, to disturb our domestic peace and tranquility, and persistently refused to comply with their express constitutional obligations to us in reference to that property, and by the use of their power in the Federal Government have striven to deprive us of an equal enjoyment of the common Territories of the Republic...

...While the subordination and the political and social inequality of the African race was fully conceded by all, it was plainly apparent that slavery would soon disappear from what are now the non-slave-holding States of the original thirteen...

...For forty years this question has been considered and debated in the halls of Congress, before the people, by the press, and before the tribunals of justice. The majority of the people of the North in 1860 decided it in their own favor. We refuse to submit to that judgment, and in vindication of our refusal we offer the Constitution of our country and point to the total absence of any express power to exclude us."

Georgia's declaration elaborates a description of the history of slavery and economy in the century before their secede. But, in terms of timing, their issues are specific. What exactly are they referring to with their "serious causes of complaint?"

In essence, it all comes down to the abolitionist movement. In the South, there were numerous uprisings against slavery by black people. This was a cause of great concern to slaveholders, especially in states where the slave population was a near-majority (or was a majority). It was a source of fear and anxiety, and one that they kept in check through restrictive laws and the threat of military force. These laws were opposed by many groups, especially by free black people living beyond the immediate influence of slaveholders.

Northern abolitionists actively opposed these laws meant to keep the enslaved population oppressed. They refused to return escaped slaves or report on them. They helped more people escape slavery. They opposed attempts to expand slavery or support it at a federal level. They generated a great deal of anger and paranoia among slaveholders that exploded when abolitionist John Brown actively armed and incited an uprising in Harper's Ferry, Virginia.

People across the South feared that Northerners would incite violence and terror to get rid of slavery in their states. They refused to even put the Republican candidate Abraham Lincoln on their ballots. But, despite their effort to keep him out of the White House, Lincoln prevailed on the back of overwhelming Northern support. The Southern states claimed that their will had been entirely subverted, and that the system favored northern extremists who influenced the government. Their answer to their claim was to create their own government.

The confederate government established a government in Richmond, just 100 miles from the Capitol in D.C., with their own Confederate constitution. There were initial hopes that the CSA could be peacefully reintegrated back into the USA. But, the cultivated fear of northern agitation led the Confederate army to be wary of U.S. activities. When the USA sent troops to secure the federal territory of Fort Sumter, the confederates demanded that the army retreat. After a lengthy standoff, the Confederates attacked the fort. This act of aggression ended hopes of a peaceful resolution and led to the Civil War.

Excerpt from:

The Confederate States of America - InfoPlease