Which of the following was not a cause of the civil war?
a. a belief in states' rights
b. blockading southern ports
c. declaration to end slavery
d. firing on fort sumter

I think the answer would be B bc slavery wasnt ending during that time

Slavery did not end until the As a result of this gradualism approach, New York did not free its last slaves until 1827, Rhode Island had seven slaves still listed in the 1840 census, Pennsylvania's last slaves were freed in 1847, Connecticut did not completely abolish slavery until 1848, and slavery was not completely lifted in New Hampshire and New Jersey until the nationwide emancipation in 1865.

so your answer is C)
 hope i helped