Final answer:
The bombardment and subsequent surrender of Fort Sumter were pivotal as they represented the Confederacy's first aggressive military move against the Union, provoking President Lincoln to respond, which escalated into the Civil War.
Step-by-step explanation:
The incident at Fort Sumter was a turning point for the Civil War to begin because it marked the first time that the Confederacy took decisive military action against the Union by bombarding the fort. Confederate forces in Charleston began the bombardment of Fort Sumter on April 12, 1861, and after two days, the Union garrison surrendered. President Lincoln had previously made it clear that the Union would defend its territories, and by the act of aggression towards the Union forces at Fort Sumter, the Confederates effectively started the war. Lincoln responded by calling for troops to put down the rebellion, leading to further secessions and the full-scale escalation of the conflict. This confrontation signified the point of no return, making clear the Confederate resolve to assert their independence and the Union's commitment to preserving the nation's unity.