Final answer:
The southern states threatened to secede if Abraham Lincoln won the Election of 1860 because they believed he would not uphold the practice of slavery, threatening their way of life and economic interests. The ensuing Secession Crisis and formation of the Confederate States of America ultimately led to the Civil War.
Step-by-step explanation:
The southern states threatened to secede if Abraham Lincoln won the Election of 1860 not because they thought he would continue the practice of slavery, but because they believed he would not continue to uphold it. The possibility of Lincoln's presidency and the Republican Party's opposition to the expansion of slavery into new territories posed a direct threat to the southern way of life and their economic interests, which relied heavily on slave labor.
The belief that a Lincoln presidency would lead to the end of slavery led to the Secession Crisis, where states began to organize secession conventions right after the election results were announced. The Republican commitment to keeping slavery out of the territories and the suspicion that abolitionists would use violent measures similar to John Brown's raid contributed to increasing tensions.
Ultimately, this led to the secession of southern states and the formation of the Confederate States of America, which prioritized maintaining and expanding slavery, thereby leading to the Civil War. Seven states from the Lower South seceded before Lincoln's inauguration, convinced that the federal government's failure to enforce the Fugitive Slave Act was indicative of a future where their states' rights and institution of slavery were under imminent threat.