Final answer:
The attack on Fort Sumter by Confederate forces in 1861, due to escalating tensions over resupplying the fort, marked the start of the American Civil War. Its strategic location and symbolism made Fort Sumter a key stronghold, its fall signaling the divide between the North and South.
Step-by-step explanation:
The circumstances at Fort Sumter in 1861 were pivotal in sparking the beginning of the American Civil War. The strategic importance of Fort Sumter was due to its location in Charleston, South Carolina, the South's most vital Atlantic port. A Union garrison of fewer than one hundred men was stationed there, which the Confederacy saw as a vulnerable target. Tensions escalated when President Lincoln announced he would resupply the fort, leading the Confederate forces to interpret this as an act of aggression, prompting them to fire upon the fort on April 12, 1861. This attack marked the onset of the Civil War as it forced the issue of Union authority versus states' rights into armed conflict.
Fort Sumter was an important stronghold because of its strategic positioning, enabling control over the entrance to Charleston Harbor. Moreover, it became a symbol of national authority as the Confederacy sought to assert its independence and the Union strove to maintain its sovereignty over the rebelling states. The bombardment and subsequent surrender of Fort Sumter served to solidify the divided loyalties of states and spurred the North and South into a prolonged and bloody conflict.