what was the major cause of the civil war?

it's a truly simple question, it can go in a number of directions...
so i'm gonna go with the north and south having different opinions on whether owning slaves is moral and allowed in the const. and things like that.

but. i need a good thesis statement. anyone willing to help?<3??!

::::edit::::
i have like... 8 documents so far.
it's not that i'm not willing to do research, i just suck at starting my paper.