Except this is just a convenient fiction. Pro-slavery southerners invaded Kentucky and overthrew the duly elected government because Kentucky (despite being a slave state) refused to seceed. Kentucky's "Articles of Secession" are a fiction. This and the firing on Fort Sumter took place merely as a response to Lincoln's election, not any actual action taken against southern interests.

The build up was a long one with the southern states systematically chipping away at the rights of northern states via a stacked Supreme Court and their un-democratic over-representation in the House (sound familiar?). They pushed laws that required that slaves be returned to their masters, even from jurisdictions that prohibited slavery.

They also pushed through a SCOTUS ruling that overrode the no-slavery laws of the local state, which allowed people to claim residency in a southern state, import slaves into a non-slave state, and essentially rendered the non-slave state powerless to do anything about it... an early form of regulatory arbitrage (sound anything like "sell insurance across state lines"?) In one fell swoop this effectively brought slavery back into the entire United States.

The southern states, southern politicians, and southern business leaders actively campaigned to expand the reach of slavery as far as possible, even agitating for Manifest Destiny policies to seize new pro-slavery territory. They opposed the Missouri compromise and the southern-packed SCOTUS obliged, ruling that the territories couldn't disallow slavery.

The southern states were far from passive little children just minding their own business, being bullied by the mean old north. They believed in slavery so strongly they attempted to use every means possible to force it on everyone, expand its scope, and silence anyone who opposed it (after all, pre-incorporation the first amendment didn't apply to states and you could be jailed for having an anti-slavery opinion in the south or for importing/printing anti-slavery books - and many people were!)

While I'm here, let us run down another convenient myth that "the war wasn't really about slavery", which I shall now destroy by _quoting the confederate's own words_ which is proof-fucking-positive that the war was absolutely 100% about slavery.

--

The Mississippi Declaration of Secession states: "In the momentous step, which our State has taken of dissolving its connection with the government of which we so long formed a part, it is but just that we should declare the prominent reasons which have induced our course.

Our position is thoroughly identified with the institution of slavery - the greatest material interest of the world."

--

South Carolina's Declaration of Secession: "We affirm that these ends for which this Government was instituted have been defeated, and the Government itself has been made destructive of them by the action of the non-slaveholding States. Those States have assume the right of deciding upon the propriety of our domestic institutions; and have denied the rights of property established in fifteen of the States and recognized by the Constitution; they have denounced as sinful the institution of slavery; they have permitted open establishment among them of societies, whose avowed object is to disturb the peace and to eloign the property of the citizens of other States. They have encouraged and assisted thousands of our slaves to leave their homes; and those who remain, have been incited by emissaries, books and pictures to servile insurrection."

--

Georgia's Declaration of Secession: "The people of Georgia having dissolved their political connection with the Government of the United States of America, present to their confederates and the world the causes which have led to the separation. For the last ten years we have had numerous and serious causes of complaint against our non-slaveholding confederate States with reference to the subject of African slavery."

--

Texas Declaration of Secession: "Texas abandoned her separate national existence and consented to become one of the Confederated Union ... She was received as a commonwealth holding, maintaining and protecting the institution known as negro slavery - the servitude of the African to the white race within her limits - a relation that had existed from the first settlement of her wilderness by the white race, and which her people intended should exist in all future time."

--