The constitution provides for war. Its drafters never foresaw a civil war and did not include provisions for this. You could say Lincoln accepted the secession but then waged a war to recapture the seceded states.
You're right. It does. But the Congress was supposed to have something to do with it. The way things were set up the President was supposed to follow the orders of Congress. Lincoln changed all that. Don't you just love it?
ML/NJ