Lincoln won the Election of 1860 because of his popularity amongst the Republicans in the North. When this was announced in the South, many southerners became upset and believed that the President and Congress were set against their interests. After this event, many southern states came to favor secession.
I am honored to be the 16th president of the United States of America.
The South definitely does not like me. They see me as a threat to slavery...
States had already began to secede by the time Lincoln took office. The states that had left the Union called themselves the Confederate States of America. Lincoln had warned the seceded states in his inaugural address about what they were doing and said that he didn't have any intention on interfering with the institution of slavery's existence.
The South rejected what Lincoln had to say and took over post offices, forts, and other federal property that was within their borders. Lincoln was worried about Fort Sumter and didn't want to give it up, but later Confederates captured the fort while it was isolated. This attack on Fort Sumter marked the beginning of the American Civil War. More states seceded after this and people in the North became ready to fight.