Final answer:
When Abraham Lincoln won the election of 1860, South Carolina declared its secession from the Union, leading to the formation of the Confederate States of America and the start of the Civil War.
Step-by-step explanation:
When Abraham Lincoln won the election of 1860, South Carolina declared its secession from the Union. On December 20, 1860, the South Carolina convention voted unanimously to dissolve their Union with the United States. This decision was followed by six other southern states that also seceded, ultimately leading to the formation of the Confederate States of America and the beginning of the American Civil War.