All this talk about the “balance of power” between “the North” and “the South” overlooks that without slavery, there would not be a “North” and a “South”. As geographical expressions, sure–the more northerly and the more southerly states–but the thing that divided the states into distinct and hostile blocs was the existence of slavery in some states but not others. The South did not have a separate language–Americans didn’t fight the bloodiest war in our history over the difference between “y’all” and “yinz”. Nor was there some deep-seated religious dispute; both the free states and the slave states were, by the mid-19th Century, pretty devout, and mostly Protestant; with major denominations shared in both the northern and southern sections of the country (Baptist, Methodist, Presbyterian) dividing over slavery (not over the Filioque clause or the fine details of justification or any other theological arcana) in the run-up to the war or after secession. The thing that united the states from Virginia to Texas, while distinguishing that group of states from both the old northeastern states like Massachusetts or the new midwestern states like Iowa, was the continued existence of slavery in the states in the southern half of the country.
Nor were the free states some monolithic land of factories; even now much of the Midwest is an agricultural region, and that was even more so in 1860 (for example, Detroit had obviously not yet emerged as a world center of automobile production). The non-slave areas of the United States included a variegated economy of growing numbers of factories alongside many farms. The slave states, on the other hand (especially the Deep South states, which not coincidentally were the first states to secede) was dominated by a form of “agrarian economy” characterized not by Jeffersonian yeoman farmers growing food to feed their own families, but by large capitalistic plantations producing commodity goods for international trade. Of course there were many small farmers in the slave states (and butchers, bakers, and candlestick-makers), but the central engine of the economy of the slave states were the plantations–in 1860, cotton easily accounted for the majority of all U.S. foreign exports. And that Southern plantation economy relied entirely on slavery.
The Southern economy was massively dependent on plantations employing slave labor, in the way that some places are dependent on oil: Even though not everyone owns an oil well, if the price of oil drops, the East Texas Cadillac dealers or sellers of cowboy hats suffer along with the oilmen. If the basis for the plantation economy–the system of slave labor–were disrupted, there would be severe economic hardship throughout Southern society, not just among wealthy planters with lots of slaves. (Again not coincidentally, areas of the south like East Tennessee or the northwestern areas of Virginia, which were not as heavily involved in the plantation economy, were hotbeds of Unionism, with northwestern Virginia seceding from the secession to become Unionist West Virginia.) On top of (a Marxian would no doubt say as a result of) these economic factors you had a whole social and ideological system of white supremacy, and (especially in places where a large percentage or even the majority of the population were slaves, which included the entire states of South Carolina and Mississippi), there were deep seated fears of slave rebellion and the potential for social and political chaos as a result.
By contrast, the non-slave-holding states were increasingly not merely uninvested in and uninterested in slavery, but actively hostile to it. One need not be a believer in full racial equality in order to sympathize with people systemically deprived of all social and political rights, and one need not have felt even a condescending sympathy for the blacks in order to oppose slavery. Slavery was increasingly seen as being blatantly incompatible with the ideals on which the Republic was founded; and there were fears of the “Slave Power” as an alien, aristocratic, un-American threat to the ideals of free labor and republican self-government. By and large the citizens of the free states weren’t prepared in 1860 to wage a crusade to abolish slavery in South Carolina, but they were hostile enough to slavery to want to see it “contained”, like a plague (or like Communism a century later). And the free staters were hostile enough to slavery to elect an openly anti-slavery man (though not a “radical” immediate abolitionist) to the presidency.
You can say the free states and the slave states should have compromised, but in fact the first half of the 19th Century was marked by repeated attempts at just that. In early 19th Century American politics, “compromise” was bandied about as a fine and noble word, and very often over exactly the issue of slavery, from the Missouri Compromise to the Compromise of 1850. It may be that the issue of slavery simply isn’t very compromisable–people are either slave or not; it is (if you’ll forgive the phrase) a black and white issue. And of course it was the slave states which forced the issue far more than radical free state abolitionists, forcing the end of the Compromise of 1850, touching off “Bleeding” Kansas, the precursor civil war to the Civil War, and causing even many moderate citizens of the free states to fear an aggressive, expansionist “Slave Power” that had to be stopped by putting the new anti-slavery Republican Party in power. That in turn led to the secession of eleven of the fifteen slave states (with two others being divided between Confederates and Unionists–the Confederacy formally claimed both Kentucky and Missouri–and serious pro-Confederate sympathies in Maryland), and the outbreak of civil war.
Without slavery there might at some point in American history have been a civil war, but it was slavery which brought about the Civil War. There surely would have been tensions and disputes over central versus local authority, as there almost inevitably will be in any federal system. Personally, I think open and bloody warfare would have been much less likely without an issue as morally stark as slavery versus freedom.
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