Short Answer 
The election of Abraham Lincoln alarmed the South due to his opposition to slavery’s expansion, which threatened their economy reliant on slave labor. Concerns over potential economic turmoil and loss of political power under a Republican government heightened fears of diminished states’ rights, leading to the eventual secession of Southern states and the Civil War.
1. Opposition to Slavery
The election of Abraham Lincoln was alarming to the South because he and the Republican party opposed the expansion of slavery into newly acquired territories. While Lincoln did not call for immediate abolition, his presidency signified a growing anti-slavery sentiment that threatened the Southern economy, heavily dependent on slave labor. The South’s fear stemmed from the belief that this opposition would undermine their social and economic structures.
2. Economic Impact
The Southern economy was tightly woven with the institution of slavery, particularly in agriculture. The South anticipated that if there were any moves towards abolishing or restricting slavery, it would lead to disastrous economic consequences. This included potential declines in profits from crops and a significant loss of labor, which were major concerns for Southern states reliant on slave-based agricultural practices.
3. Political Power and States’ Rights
The election of Lincoln meant that the Republican party, viewed as antagonistic to Southern interests, would control the executive branch of the federal government. Many Southerners were concerned that the party would enact policies diminishing their political power and infringing on their rights. This fear extended to a belief that a Republican-led federal government would curtail their states’ rights, especially regarding slavery, leading to tensions that sparked the eventual secession of Southern states and the onset of the American Civil War.