"Was the civil war about slavery or was it about states rights?"

A common explanation is that the Civil War was fought over the moral issue of slavery. In fact, it was the economics of slavery and political control of that system that was central to the conflict. Many maintain that the primary cause of the war was the Southern states' desire to preserve the institution of slavery. Others minimize slavery and point to other factors, such as taxation or the principle of States' Rights.

Explanation:

The American Civil War was fought between the United States of America and the Confederate States of America, a collection of eleven southern states that left the Union in 1860 and 1861. The conflict began primarily as a result of the long-standing disagreement over the institution of slavery.

could you give me the options ?

a.

congress passed laws allowing for free passage between states.