What event marked the beginning of the Civil War?

The firing on Fort Sumter is recognized as the event that marked the beginning of the Civil War because it represented the first military engagement between the Union and Confederate forces. On April 12, 1861, Confederate troops fired upon the Union-held fort in Charleston Harbor, South Carolina. This action was a decisive moment in American history, as it escalated tensions that had been building over issues such as states' rights and slavery into open conflict.

Prior to this event, the nation was already divided, but it was the attack on Fort Sumter that prompted President Lincoln to call for troops to suppress the rebellion, effectively signaling the start of the Civil War. The other events listed, while significant in the context of the war (for example, the Battle of Gettysburg was a turning point and the Emancipation Proclamation was crucial for the abolition of slavery), occurred after the war had already begun. The firing on Fort Sumter is the pivotal moment that initiated the hostilities, making it a key historical reference point for the start of the Civil War.