January 1861 -- The South Secedes.
When Abraham Lincoln, a known opponent of slavery, was elected president, the South Carolina legislature perceived a threat. Calling a state convention, the delegates voted to remove the state of South Carolina from the union known as the United States of America.
The secession of South Carolina was followed by the secession of six more states -- Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas -- and the threat of secession by four more -- Virginia, Arkansas, Tennessee, and North Carolina. These eleven states eventually formed the Confederate States of America.
All of them had been talking about and threatening to go to war if Lincoln or anyone who was not pro-slavery were to be elected. The newspapers of the time were full of quotes about it to numerous to post them all here.
February 1861 -- The South Creates a Government.
At a convention in Montgomery, Alabama, the seven seceding states created the Confederate Constitution, a document similar to the United States Constitution, but with greater stress on the autonomy of each state. Jefferson Davis was named provisional president of the Confederacy until elections could be held.
February 1861 -- The South Seizes Federal Forts.
When President Buchanan -- Lincoln's predecessor -- refused to surrender southern federal forts to the seceding states, southern state troops seized them. At Fort Sumter, South Carolina troops repulsed a supply ship trying to reach federal forces based in the fort. The ship was forced to return to New York, its supplies undelivered.
This action by Buchanan only reafirmed the precedent that was set by previous Presidents when it came to dealing with States that had allready tried to remove themselves from the USA. (Jackson was not the first to deal with this kind of thing eaither btw)
March 1861 -- Lincoln's Inauguration.
At Lincoln's inauguration on March 4, the new president said he had no plans to end slavery in those states where it already existed, but he also said he would not accept secession. He hoped to resolve the national crisis without warfare. Where all the south at the time could talk about was going to war.
April 1861 -- Attack on Fort Sumter.
When President Lincoln planned to send supplies to Fort Sumter, he alerted the state in advance, in an attempt to avoid hostilities. South Carolina, however, as you mentioned saw the fort as too strategic. Robert Anderson, (The forts legal commander of the time)was asked to surrender immediately. Anderson offered to surrender with terms, but his offer was rejected, and on April 12, the Civil War officially began with shots fired on the fort.