Answer:
a. True
There has been debate about the causes that were behind the start of the Civil War. Some say it was not so much about slavery as about states' rights. Actually, both issues explain why the Civil War was fought. A central reason why some states asserted their rights to leave the Union was because of the issue of slavery.
"Declarations of Causes" documents issued by some of the Confederate States demonstrated that both slavery and states' rights were major reasons behind the secession movement. The states that seceded felt it was not the business of the northern states to tell them how to run their economies (including the issue of using slaves).