Am i correct i this question? im not so sure

what is the main idea of this excerpt from abraham lincoln’s second inaugural address?

one eighth of the whole population were colored slaves, not distributed generally over the union, but localized in the southern part of it. these slaves constituted a peculiar and powerful interest. all knew that this interest was, somehow, the cause of the war. to strengthen, perpetuate, and extend this interest was the object for which the insurgents would rend the union, even by war; while the government claimed no right to do more than to restrict the territorial enlargement of it.

a.
slavery was the main cause of the civil war. (my answer)
b.
landowners had no right to enslave humans.
c.
slavery only benefitted rich landowners.
d.
the south started the practice of slavery.