When did states succeed from the union and why?

Following Lincoln's 1860 election win, on a ticket of no new slave-states, the South saw that it would always be outvoted in Congress, which would tend to pass laws that favoured the North.

So the Confederacy began, with South Carolina seceding from the USA in December, and six more by the time of Lincoln's inauguration in March. After the firing on Fort Sumter, and Lincoln's appeal for volunteer-troops, another four states joined them, making-up the eleven states of the Confederacy.