Final answer:
Abraham Lincoln's election in 1860 led to several southern states seceding from the Union, causing the South to declare war on the North.
Step-by-step explanation:
Abraham Lincoln's election in 1860 had a significant impact on national unity. While it did not immediately heal the nation's political divisions, it led to several southern states seceding from the Union in protest. South Carolina was the first to secede, followed by other southern states such as Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas. This eventually led to the Civil War, with the South declaring war on the North.
Learn more about Abraham Lincoln's election and its impact on national unity