The correct answer is A) the Civil War.
In the United States, slavery played a major role in the Civil War.
Slavery was a key element in the Civil War. The Southern States were segregationist states that supported slavery. The Northern states, the Union states, were against slavery. Many people in the North favored abolitionism, meanwhile, in the Southern states, people did not want slavery to end. It was part of its society. President Abraham Lincoln was in favor of ending slavery.