In my previous descriptions of Presidents I've reviewed for their character - Franklin Pierce and James Buchanan - I made note of the fact that these were men caught in a tumultuous time. The 1850s was basically a decade building up to a fight between two halves of the United States: the North and the South. But even that was the final stage of a prolonged historic struggle between two opposing ideologies, two opposing economies, two opposing cultures that had been joined together in matrimony in order to make a new nation - the United States - live and breathe.
I mentioned during Buchanan's article about "the tides of history were flowing towards conflict." How much of that statement is actually true? Were the tides of history flowing irrevocably towards war between states? Was the United States doomed one way or another to fight a civil war?
The broad answer, and in some ways the simplest, is Yes.
All of history is replete with examples of nations (and empires) rising and falling, with a civil war a key component to that nation's darkest moments. To look to America's most direct ancestry, Great Britain/UK, one could count at least two civil war eras: the War of the Roses (not always counted because it was more dynastic in-fighting between cousins than a broad ideological struggle), and the English Civil War between Charles I (divine right of kings and Catholicism) vs. Cromwell and Parliament (the right of free men to self-representation and Protestantism). One of the earliest relatively documented civil wars was the Peloponnesian War, and that quite honestly did not end well for the Greeks (the Macedonians marched in after the dust settled). The Roman Republic ended with a civil war that led to an Empire, with that Empire wracked by civil wars and divisions throughout its reign until the western wing of the empire collapsed at the start of the Dark Ages. China wasn't immune to internal strife: look to the Taiping Rebellion in the 19th Century, or uprisings during the Ming dynasty. There aren't a lot of nations that don't have some form of rebellion or uprising in their placid histories: my Gods, Switzerland has at least one in recent history.
The inevitability of a civil war is another matter. The odds of it happening are quite good, but under the right circumstances - almost always through moderated leadership and a minimum of economic corruption - a nation can avoid the conditions that lead up to civil war. Even nations with histories of messy civil wars - hello again England! - can have periods of prolonged internal cooperation between tribal forces (usually because they're busy fighting the French and Germans instead).
One thing historians like to note is how a nation (or empire) forms in the first place: usually through a series of localized conflicts where a particular military or political leader can forge a national identity via military victories and successful treaties with allies that get absorbed into the growing nation. For the United States, it came about through a centuries-long period of European colonization between various powers - England, Spain, France, Netherlands - working in conflict and sometimes in concert with each other AND with native peoples who themselves were working with and against each other in a complex chain of events. That all culminated in a grouping of 13 English-controlled colonies that realized one day they and their British overlords really couldn't comprehend each other and that the colonies were a completely separate "race" of people.
The colonies were forced by necessity to ally with one another to make a strong case to other nations that they were a separate nation in rebellion against England ("Hang together else hang separately," to paraphrase the wise man). The original form of national government - a confederation - simply didn't work, threatening a split then and there (and a possible future where the separated states became the Third World states - puppets - to the Euro powers): the response was to form a stronger federal system under the Constitution, which still gave the states identity and power... and seeding the future conflicts that would arise from the cultural and economic differences that existed even then.
At nation's birth, the nation had its sections: The North mostly maritime and merchant based economies - and later an industrial economy - that required strong finances, high tariffs, an eye to foreign dealings, and a reasonably open class system between poor, middle and wealthy. The South was mostly agriculture - first tobacco, then cotton - with a focus on low tariffs, internal politics, and a strict division of class between rich and poor (and white and black). The spread into the Midwest and West created other geographic cultures, but North and South dominated and reflected as such during the westward expansion: the Midwest in particular influenced by the industrial economics that originated in New England / Upper Atlantic states.
The divisions between North and South flared up at key moments in American history: the Alien and Sedition Acts (when the idea of state nullification first appeared); the War of 1812 (when northern states refused to support a war backed by Southerners and then-Western states); the issue of letting slavery spread into territories (resolved first by the Northwest Ordinance which kept the northern territories free-state no matter what, then by the Missouri Compromise by 1820); and then the tariff fighting of 1832 (where Jackson resolved it by offering a lenient tariff deal with the very strong suggestion to John C. Calhoun that Calhoun would hang if he didn't agree to the deal). It says a lot that Jackson himself noted: "the tariff was only a pretext, and disunion and southern confederacy the real object..." (reference: Correspondence by Andrew Jackson, vol. 7, p. 72) Even he could see what was coming...
So, in the simplest sense, there was always a good chance the United States would have faced a civil war at some point in its history. The deal was, it didn't have to: wise leadership (an Active-Positive like James Monroe) could have resolved tensions between extremists to let the moderates have their day; forceful leadership (an Active-Negative with an attitude to boot) could have resolved tensions by hanging the SOBs itching for disunion (pretty much one of the few things Andrew Jackson was right about).
By the 1850s the political elites of the Democratic party were not beholden to moderates or pragmatists: they were beholden to wealthy Southern plantation/slave owners who represented an increasingly smaller portion of the nation's population while holding much of its lopsided wealth. In terms of moderate leadership there were a handful - Stephen A. Douglas the most likely candidate - but too few and far between. Worse, leaders on the national stage were increasingly incapable of controlling forces at the state level (not without the force needed to impose such will). And in terms of forceful leadership, the only ones in the Democratic ranks were clearly on the side of slavery by that decade: and the problem was, slavery was a losing argument...
Slavery was a losing argument because the population of the overall nation was leaning more and more towards Free-State beliefs. This can be clearly noted by the population trends of 1850 and 1860: Northern states were increasing their population numbers (with a solid boost via immigration) while the Southern states were relatively stagnant. This had a serious impact on their representation in the House of Representatives, based on population proportions. One of the early ironies was that the South benefited from their Three-Fifths Rule counting non-voting slaves, which helped them dominate the House for almost 70 years: by 1860 the slaves outnumbered whites in some places which meant the lack of full counting hurt Southern states that failed to keep control of Congress. And there's a reason why Lincoln won a clear Electoral victory in 1860 without even having his name on the ballot in most Southern states: the Electoral count for Northern (New York: 35, Pennsylvania 27 and Ohio 23 the top three) and Midwestern states dwarfed Southern states (the top three were Virginia 15 Kentucky 12 and Tennessee 12... and they went for a pro-Union candidate).
Another reason slavery was a losing argument was because the western territories - acquired through war - wasn't as fertile a place for a slave-based agriculture that the slave owners desired. Cotton was a land-hungry crop: they needed to spread but were confined first by law (the various Compromises) and then by culture (there would be no way the Free States of the North would allow slave-owners to set up slave plantations in oh, Illinois or Iowa). When California went quickly to Free State - the one place between Texas and the Pacific where cotton could conceivably grow - the cotton growers were running out of options.
The final reason slavery was a losing argument was "the tide of history": the Christian Awakening movements of the 18th and 19th Century brought with it a spiritual push that lent itself well to the abolitionist movement not only in the Northern states but also in places like England: when Great Britain abolished slavery across its empire, slavery on a global scale - the British Navy put a serious crimp on the African slave trade from 1833 on - was doomed.
Was a civil war unavoidable by this point (the 1850s)? Possibly... like I said it would have involved the right leadership and the best decision-making. But in the real world, both are rare. So a civil war over a divisive sectional issue - slavery - was due.
Could either side - North or South - done more to avoid war? In most respects for the North, No. Politically, they had bent over backwards on various issues such as the Mexican-American War, the Fugitive Slave Acts, and previous compromises for decades with no sign that the Southern slave-owners were placated with each deal. The Fugitive Slave Act was being abused to Northerners' disgust. And the Dred Scott decision overreached by trying to negate Northern states' rights to define citizenship. To the North, if they said as a whole "enough was enough" I wouldn't blame them.
In most respects for the South, I would say "yes". Their over-reliance on a single crop - cotton - proved in the long-term to be a bad idea: not only during the civil war when they had no usable land to grow food, but also afterwards when they kept cotton as the primary crop until the boll weevil invasion of the early 20th century proved they were better off with a diversified crop system. They could have implemented an employment model that didn't rely on slavery (the costs of maintaining a slave compared to maintaining a paid employee: what honestly would have been the difference back in the 19th Century before worker unions?). Northern politicians - even abolitionists - offered up the idea of paying slave owners federal money to voluntarily free their slaves, getting reimbursed with each slave freed. Manumission could have, in hindsight, gone a long way towards ending slavery without the South's economy getting wrecked or their cultural heritage (outside of Mighty Whitey attitudes) shredded.
I would have said yes but the Southern culture forced an arrogant No as their answer. Cotton was the only crop they knew and the source of their political oligarchy's power/wealth: growing other crops (you know, barley could have helped the microbrewery market in the Southeast a century before it caught on) was seemingly beneath them. Decades of winning major compromises over Northerners, and having pro-slavery Southerners in key federal government positions made slave-owners cocky and reckless. And worse of all, the Southerners feared their slaves even as they perpetuated the desire to own them. Slave uprisings in Haiti convinced Southerners that given the chance their African black slaves would rise up and enact vengeance for all the wrongs the White Southerners enforced upon them: Nat Turner's uprising merely confirmed such fears. And John Brown's attempted raid at Harper's Ferry by 1859 to get Virginian slaves to rise up was for the slave-owners the real start of the 1860 civil war. What can you say about a culture that feared something so much (their slaves) that they couldn't even consider an alternate possibility (gradual end of slavery via manumission) that could have resolved that fear without bloodshed?
This isn't the clearest argument one way or the other, I know. This is the best that I can say it:
There is, by the by, an ongoing blog about Disunion in the New York Times discussing the march towards civil war and its influence then and now. It's worth a read.