Final answer:
The firing on Fort Sumter marked the official start of the Civil War.
Step-by-step explanation:
The firing on Union-held Fort Sumter by white Southerners is considered to be the official start of the Civil War. This event took place on April 12, 1861, and it marked the beginning of the conflict between the Union (Northern states) and the Confederacy (Southern states). The Confederates, led by General P.G.T. Beauregard, bombarded the fort and eventually forced its surrender. This action by the Confederates was a significant step towards the start of the Civil War.
Learn more about Start of the Civil War