No, it started out as a secession and Lincoln had not called for troops. The South turned it into a war which turned it into a rebellion.
Then Lincoln called for troops.
It started as a trade war. The fed was financed by tariffs of which a very significant percentage, 75%, was collected in southern ports. The fed used the ports to enforce the laws. If the south had any hope of secession they had to control their ports and the collection of tariffs. The north obviously could not afford to permanently lose that revenue.
The north via tariffs engaged in economic oppression of the south. Slavery was just one narrative that both sides manipulated to sway support their way.