There are several things going on here.

What we know superficially about South Carolina is that the state's political culture was dedicated to the defense of slavery, and also sought to keep tariffs relatively low for its own interests. It was dominated by elite planters who believed that their status as patriarchs gave them the right to rule in their communities, their state, and their nation. But we can make similar claims about other southern states that don't seem to have been as radical. So what was going on with South Carolina?

Part of this, as with so many things, comes down to geography and soil geology, which influenced the state's economic development. The economy of early colonial South Carolina, like many plantation colonies, was characterized by the growth of cash crops. In South Carolina's case, the two main ones were indigo and rice. Indigo was a particularly capital-intensive crop, and rice cultivation required planters to dam up large amounts of water to irrigate the rice fields, which required a lot of land, and large amounts of labor. These are not crops like tobacco, that in a relative sense were less labor and capital intensive. What this meant for South Carolina was that it developed a coherent elite culture relatively early on; South Carolina's crops were most profitable when grown on a large scale, so unlike Virginia, which had a reasonably large social tier of middling planters in addition to its elite, the colony built a relatively small ruling class that was extremely wealthy. Because the swamps around Charleston are extremely unhealthy, this elite class spent much of its time in Charleston itself where it was much safer. South Carolina developed a wealthy and influential ruling class early, and in the context of a society that had an overwhelmingly large enslaved population, as high as 85% of the whole population in some places by 1830.

When we get to the South Carolina upcountry, things get more complicated, but some of the same things are still at play here. The invention of the cotton gin, yes, was a major game-changer here. This device finally made the short staple cotton grown further inland profitable - previously the only cotton you could grow effectively was long staple, which only grew well along the coastline. With the cotton gin came also, you guessed it, plantation slavery. What this meant was that the upland regions produced a plantation class dedicated to the defense of slavery that, after a time, became not too different from their lowcountry counterparts. Unlike a state like Virginia, for example, the distinction between the upper and lower portions of the state was never as dramatic. This permitted South Carolina to develop a political culture that ran on consensus; there wasn't a whole of lot of internal dissent among the ruling class. They basically agreed on the main central questions, like preserving slavery and keeping the forces of popular democracy in check. Remember, South Carolina was still awarding its Electoral College votes on the decisions of its state legislature even up to 1860. As early as the colonial period, South Carolina developed a convention that dissent in the legislature on a measure bound to pass was to be voiced not through a negative vote, but through abstention. It was a society that ran on the pretense of elite unanimity.

This elite consensus was actually quite important. Even before the development of modern infrastructure, South Carolina was a pretty small state. Elites by and large all participated in the same institutions, were reared with the same values, and had similar economic interests. There just weren't all that many places to go within the state. By 1860, over 96% of the state's population had been born within the state itself. This consensus, which permitted the state to project something of a united front, also led to a degree of parochialism that people commented on even at the time. As the 19th century progressed, there does seem to have been a real sense of social decline and cultural inferiority in the state that its leadership lamented, and a view that the state's best days were behind it. The Carolina elite had long fancied themselves the heirs to English aristocracy, but in the view of South Carolina's own William Henry Trescot, they were becoming more prone to "fierce impatience," "petulant suspicion," "rude and unnatural arrogance," and "noisy boastfulness." In the face of potential decline at home and an ever more prosperous North, Carolina's elite was developing a hair-trigger fightiness that made them prone to conflict.

South Carolina thus had both an internal political culture built on consensus on key issues that permitted it to advance its interests on the national stage in a relatively unified way. It was also a state that was becoming increasingly unsure of itself as the elites, long wedded to 18th century ideals of status and orders, found themselves confronting a world leaving those values behind. This generated an unsureness, and a willingness to lash out. It is important also not to understate the importance of masculinity and honor culture in all of this either. It is no accident that one of the events leading up to the Civil War, the caning of US Senator Charles Sumner, occurred at the hands of South Carolinian Preston Brooks, who stepped in to defend the honor of his kinsman, the South Carolinian Andrew Butler. As William Freehling put it:

[South Carolinians] were half-cocky about consolidating the old. They half-despaired about battling the new. Somewhere in the swings between one of the most debilitating inferiority complexes in nineteenth century America and one of the most soaring superiority complexes any ruling class will ever develop lay that appalling eccentric, the South Carolina would-be revolutionary.

-Road to Disunion, Vol 1, p. 252

Readings:

William Freehling, The Road to Disunion, Secessionists at Bay, 1776 - 1854

Kenneth Greenberg, Masters and Statesmen, the Political Culture of American Slavery

Bertram Wyatt-Brown, Southern Honor: Ethics and Behavior in the Old South

Stephanie McCurry, Masters of Small Worlds: Yeoman Households, Gender Relations, and the Political Culture of the Antebellum South Carolina Low Country

Manisha Sinha, The Counterrevolution of Slavery: Politics and Ideology in Antebellum South Carolina

Lacy Ford, Jr., Origins of Southern Radicalism: The South Carolina Upcountry, 1800 - 1860

James Oakes, The Ruling Race: A History of American Slaveholders