Because Lincoln had won the election of 1860 on a ticket of no new slave-states.
This meant that the South would always be outvoted in Congress.
The Southern States seceded from 1860-1865, during the course of the Civil War.
December 20, 1860
The Southern States did not secede until 1860 due to the work of Henry Clay, "The Great Compromiser". His efforts included things like the Compromise of 1850 and the Kansas-Nebraska Act.
South Carolina was the first to secede in 1860
Florida and South Carolina were the only Southern states to secede in 1860. The other 9 seceded in 1861.
Abraham Lincoln
Abraham Lincoln
Abraham Lincoln was elected in 1860 and states began to secede.
December 1860, as soon as it heard the result of Lincoln's election as President. Incidentally, it did not just attempt to secede. It did secede, followed by ten more Southern states.
Lincoln vowed to outlaw slavery
The election of Abraham Lincoln as President of the United States in Nov. 1860.
The first state to secede was South Carolina in December 1860. The last to leave the Union was North Carolina in May 1861.