From my files on the CW, here is a bit more nuanced approach to why the war came and what it accomplished.

For a brief discussion on the who and the when of causal analysis, you may also be interested in "Civil War Historiography 101" (here)

Participation, Equality and the Constitution:
The Issues of the Civil War Era

During the restive middle decades of the nineteenth century, a series of disparate political fevers swept across the national landscape. Two separate but oftentimes complementary impulses, the Age of Democracy and the Age of Reform, produced a national crisis of identity in the form of a sectional division. The Civil War, the point at which the fever of sectional strife reached a near-lethal level, proved to be a defining moment for the American experiment in popular government. Hastened by the question of slavery in the western territories, the war preserved a unified nation and resolved several fundamental questions concerning the nature of the Union. The violence also marked a crossroads in the way in which citizens perceived their political leaders and interacted with their government.

The near-consensus of modern historiography identifies race and equality as the engine of disharmony and division between the North and the South. The truth, undoubtedly, is much more complex than a mere contest between two Americas, one slave and one free. Many complicated movements, inclinations and developments contributed to the ultimate catastrophe of internecine warfare. The primary issues of the age regularly intersected and then often divided again, leaving a more complicated trail of controversies and questions. The enduring debate concerning the nature of the Constitution was inextricably linked to the evolution of participatory democracy, which exposed for many the inherent hypocrisy of racial and gender inequality. However, in the final analysis, it is difficult to transcend the overshadowing presence of the slavery question.

As the American citizenry expanded and engaged in the multifaceted political dialogue, the Enlightenment-based ideology of republicanism gave way to a notion of democracy informed by Romanticism. Along with the dramatic changes in the way Americans approached politics, the market revolution reconstituted the American economy and forever transformed its culture and ethos. Amidst the convulsions accompanying the simultaneous reworking of the economy and the realization of popular rule, individuals eagerly embraced various programs for personal and societal amelioration. Drawing strength from a broad-based religious revival, the activists of the Age of Reform proposed and pursued a radical remaking of American society through the gospel of good works and humane values. A product of the Reform generation, the abolitionist movements of New England attempted to eradicate slavery through moral suasion. While the abolitionists may have awakened citizens to the contradictions inherent in American self-government, the movement to convert the nation to racial equality proved quixotic. The pure impulses of the first abolitionists yielded little progress toward ending slavery in the United States. Their lack of success led the movement to splinter, and several strains of abolitionism inhabited the periphery of American politics during the 1840s and early-1850s—rarely, if ever, playing a primary role in the formation of national policy.

Yet, portions of the abolitionist sentiment formed the core of a more self-interested political philosophy: free labor ideology. Influenced by contemporary economic theory more than humanitarianism and political thought, the free labor movement attached itself to the emerging message of the “American dream.” Americans triumphed, declared the common sentiment, through self-discipline, intelligence and hard work. The idea of “rugged individualism” characterized the archetypal American success story. Fueled by the Market Revolution, the free labor cause argued that slavery was a drag on the economy and an obstacle to upward mobility. The free labor movement appealed to the masses where the judgmental and apocalyptic abolitionist exhortations had not. Free labor ideology drew from adherents of the Free Soil position, which stated that slavery must not be allowed to expand into the West, without requiring an enlightened perspective on race. In fact, the free labor surge welcomed racists who did not want to share the potential of the frontier with any African Americans, free or slave. Founded on economic interests, the new philosophy produced a powerful coalition, which quickly evolved into an antislavery majority in the North. As the antislavery coalition first gained attention and then strength in the North, Southern slaveholders rallied around the defense of their peculiar institution as a positive good and a right guaranteed them by the Constitution. From the beginning of the Constitutional era, Southerners had been instrumental in protecting the notion of state supremacy. From John Taylor of Caroline to John C. Calhoun, Southern thinkers assiduously and brilliantly articulated the rights of states and defined the limits of the central government. Founding fathers James Madison and Thomas Jefferson made a significant contribution to the state rights canon with their “Resolutions of 1798,” which would later form the basis of the nullification movement of the early-1830s. The Republican Revolution of 1800 temporarily alleviated the need for resistance, and Jefferson and Madison put away their radical rhetoric of state defiance as they assumed control of the federal government. The Southern-initiated Constitutional crises would come decades later.

Resting on the power of the Democratic Party, Southerners dominated the presidency, the Senate and the Supreme Court during the first half of the nineteenth century. After the Virginia Dynasty expired and as Andrew Jackson’s powerful intersectional coalition began to fade, Southerners found themselves in an increasingly precarious political position. By the mid-1850s, as a result of disproportionate population growth in the North and West, the Jefferson-Jackson coalition faced a calamitous realignment. The Republican party, founded in 1854 on a free soil and free labor platform, gained a majority in the northern states by 1856. The new party threatened to carry the national elections and assume power completely independent of Southern support. The South equated Republican rule with the end of slavery and the abrogation of their fundamental Constitutional guarantee.

James Madison had argued forcefully that Constitutional government was a balance between justice and stability. Reflecting the Enlightenment principles and republican ideology of the eighteenth century, Madison presciently identified the political and economic repercussions of the market revolution. Madison initially perceived the frontier as the great bulwark of republicanism. He envisioned an independent “population of freeholders” exercising their franchise and protecting the triumph of the Revolution. However, the immense financial gains that accompanied the opening of the West after the War of 1812 transformed the economy and the political system during his waning years. The old agrarian order, essential to a Madisonian republic, was unraveling. Madison foresaw an emerging class of property-less voters who would forever pervert the political system he and his contemporaries had originally intended.

In the years following Madison’s death, the upheaval transformed the prevailing political climate in the United States, while the nation continued to expand. The Jackson era, which encompassed the Market Revolution, Manifest Destiny and the Age of Reform, marked the high-water mark for popular participation in American politics. While pursuit of economic interest had impelled the common man’s entry into the public forum, the late-1840s witnessed the temporary retreat of economic issues as primary points of debate. Instead, citizens wrestled with the disposition of the acquired western territories in the post-Mexican War atmosphere.

The advent of popular politics, combined with the rising tension of sectional division, made the 1850s a decade of tumult in Congress. As the Whig and Democratic parties divided and disintegrated, the fight for power centered on the new northern majority. The rise of the Republican Party and the triumph of Abraham Lincoln in 1860 led the states of the lower South to secede. When Lincoln pursued military means to quash the rebellion, the upper South states of Virginia, North Carolina, Tennessee and Arkansas joined the Confederacy. Lincoln and the nation faced the ultimate Constitutional question: by what means and at what price must the Union be preserved.

Lincoln pressed the power of the presidency to new heights in his crusade to preserve an undivided nation, and his administration achieved critical military and political victories. While Lincoln shouldered the comprehensive power of commander-in-chief, the Republican Congress accomplished a latent Whig economic agenda. The virtually unopposed Republicans passed laws to print greenbacks (legal tender backed only by the promise of the federal government), issued federal bonds, introduced the first graduated income tax, an excise tax and a national banking bill. They also initiated a return to a policy of protective tariffs, which would last into the twentieth century, and they passed a long-awaited Homestead Act and a bill to facilitate land grant colleges.

Viewed from the perspective of a showdown over racial slavery, the climax of the Civil War was, of course, the Emancipation Proclamation and the Constitutional amendments that followed. With the military defeat of the South accomplished, the northern-majority exercised its prerogatives of victory and dictated the terms of the reunion. Slavery was dead. The power of the Southern-based Democratic Party was broken. Southern planters could no longer block economic legislation. Southerners could no longer rely on the power of the Supreme Court to uphold a right to hold human property. The war reaffirmed the Constitution as a document instituting a perpetual Union, and Radical Republican lawmakers revised it to outlaw slavery and expand citizenship to freedmen.

Union victory settled the serious Constitutional questions that had divided the country along sectional lines. The war also changed the economic direction of the nation and decided numerous vexing political controversies that had plagued the ante bellum Congresses. The United States was free to enter the modern age with a government in full support of industry. Free labor in the North and West was protected from the threat of racial slavery. Yet, the issues of equality and justice and liberty for all Americans gained little immediate benefit with the victory of the Union in the Civil War.

Post-Civil War America retreated from the high ideals of equality and fairness. The thrill of participation and the stimulation connected with the fight to preserve the great democratic experiment receded during the latter part of the nineteenth century. The zeal of Radical Republicanism faded and succumbed to self-seeking politics. Despite the victories won on the battlefield, African Americans and American women would enter the twentieth century as second-class citizens. The swell of common interest in politics would subside in the aftermath of the war. The growing number of working people in the United States would find the “American dream” increasingly elusive in the years following the Union victory. The promise of the Emancipation Proclamation and Declaration of Independence would again be deferred and left to future generations to redeem.