Southern states that seceded immediately after Lincoln's election in 1860 did so because they had already been planning it in the event of a Republican victory. Their motivation involved what they perceived as a threat to the institution of slavery, which their economy was dependent upon. However, their secession was not the result of a quick decision. The volatile situation had been building for decades.
As the United States developed economically after independence, it evolved into two sections. The north built industries founded upon free labor, while the south formed an agrarian culture dependent upon the toil of slaves. In the free states of the north, a movement for abolition, or the elimination of slavery, began. This was anathema in the south, where abolition threatened not only the source of labor but also the social system.
A statesman named John C. Calhoun argued eloquently for the protection of the plantation system and its slave labor in the south, suggesting succession as a possible solution. However, he died in 1850 when the dilemma was still unresolved. As new territories became states and were added to the Union, questions arose as to whether they should be free states or slave states. Calhoun, for instance, strenuously opposed the admission of California as a free state. When the issue arose of whether Kansas should be a slave state or free state, violence ensued as the two factions fought it out, and the territory became known as Bleeding Kansas.
In 1856, democrat James Buchanan was elected president. Although he opposed slavery, he felt that it was protected by the US Constitution, so he attempted to keep the peace between anti-slavery and pro-slavery factions. Southern slave states warned that they would secede, though, if the 1860 presidential election was won by a Republican.
Lincoln personally was opposed to slavery, but upon his election he initially reassured the southern states that he had no intention of abolishing the institution. It was too late, though, because several states had already made their decisions. By the time Lincoln was inaugurated on March 4, 1861, seven states had already seceded from the Union. These were South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas.