Slavery is often cited as the main cause for the civil war but other problems related to political and cultural differences between the North and the South were also responsible.
Few other causes were-
Bleeding Kansas- In 1854, the government passed the Kansas-Nebraska act and asked its people to vote for their state if they wanted a slave state or free state. After many years of fighting Kansas was a free state.
Industry v/s farming- In 1800's the Northern state needed no slaves as they moved to major cities like New York and Boston and moved away from farming to industrialization. But the Southern states relied heavily on forced slave labor as they had vast farming economy.
Abraham Lincoln- He was a member of the new anti-slavery Republican Party. So the Southern states felt he was against slavery and also against the South.
White people in america didn´t see them as humans, so that allowed them to use them as slaves. This view of them being non-human allowed them to use them as tools and sell them like animals.