Final answer:
The most significant event in causing the Civil War was the issue of slavery. The debate over whether to expand slavery and the election of Abraham Lincoln added to the tension, but the attack on Fort Sumter ultimately triggered the war.
Step-by-step explanation:
The most significant event in causing the Civil War was the issue of slavery. Slavery was deeply ingrained in the Southern culture and economy, while Northern states had increasingly abolished it. The debate over whether to expand slavery to new territories led to political tensions, culminating in the secession of Southern states and the formation of the Confederate States of America.
Another significant event was the election of Abraham Lincoln as President. His victory in 1860, advocating for the restriction of slavery, fueled fears among Southern states that their way of life was under threat.
The attack on Fort Sumter in 1861 is often seen as the immediate cause of the Civil War. It marked the first military engagement of the conflict and led to the Union's call for troops, resulting in the escalation of hostilities.
Learn more about Causes of the Civil War