"We are fighting for independence, not slavery" -Jefferson Davis and other quotes like those of Robert E. Lee where he expresses anti-slavery sentiment are used to defend the idea that the confederacy was not seeking to be pro-slavery. My question is, how valid are these quotes? On top of that, it has been said that the articles each state made for secession didn't all mention slavery.

Overall, given this, what really was the cause of secession and the civil war? Thank you, this is a tough topic for me.