Final answer:
The first seven states to secede from the Union, known as the Deep South, did so due to the perceived threat to slavery and beliefs in states' rights, forming the Confederacy which led to the American Civil War.
Step-by-step explanation:
The significance of the first seven states to secede from the Union is deeply rooted in the historical context of the American Civil War. These states, known as the Deep South, moved to secede shortly after Abraham Lincoln's election due to the perceived threat Lincoln and the Republican Party posed to the institution of slavery. South Carolina was the first to secede in December 1860, with Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas following soon after. These states strongly believed in states' rights and the legality of secession, holding onto the principles of liberty that their forefathers fought for during the American Revolution. The escalating tensions surrounding states' rights and the expansion of slavery led these states to form the Confederate States of America in Montgomery, Alabama, in February 1861, ultimately sparking the Civil War with the attack on Fort Sumter in April 1861.