There was once. They were called Confederates. At the political leadership level, they were primarily Southern Democrats. The Democratic Party had split in two in the lead-up to the Civil War in 1860, and the Southern Democrats nominated John C. Breckinridge as their candidate for president. At the same time, there were many public avowals to secede (separate) from the United States if the rival Abraham Lincoln was elected president. That's what happened, and the secession movement began its successful campaign immediately.

Several books have been written on the subject of Southern nationalism in this era, usually tracing its roots back to South Carolina's secession overtures during the Nullification Crisis of 1831-32. The turning point which allowed the idea to gain more widespread support was the introduction of the Wilmot Proviso in 1846, followed by the election of a Whig president in 1848. In 1850, delegates from nine Southern states met at an event called the Nashville Convention, a response to the ongoing debate that led to the maligned (by all sides) Compromise of 1850. At this convention, many delegates advocated for the secession of the slave states from the United States, as incompatible with the anti-slavery North that made up a sizeable majority of the country's population by then.

The convention did not adopt the secession proposal, but the movement continued to grow. There were several state-level "states' rights conventions" held. By 1852, a party had been formed called the Southern Rights Party, explicitly advocating for secession. They nominated U.S. Sen. George M. Troup of Georgia as their candidate for president that year. The Democrats had nominated a Northerner, Franklin Pierce, who had well-known "Southern sympathies" but the Southern separatists didn't altogether trust him. The Whigs nominated U.S. Gen. Winfield Scott, who was a Virginian, but was also about as pro-Union/anti-separatist as they came.

The party didn't do very well in the election, though, but that can at least partially be blamed on Troup endorsing Pierce for president. Pierce won, and Southern separatists actually quite liked a lot of what he did.

I won't detail the political events that led up to the Civil War from there, but suffice it to say, Southern separatism only grew throughout the late 1850s, culminating in a (temporarily) successful separatist movement in 1860-61 and the Civil War.

Among earlier works that explore Southern separatism/nationalism in this period are:

• The Growth of Southern Nationalism, 1848–1861: A History of the South by Avery O. Craven (LSU Press, 1953)

• The Idea of a Southern Nation: Southern Nationalists and Southern Nationalism, 1830-1860 by John McCardell (W.W. Norton, 1979)

However, there is at least one academic critic of the idea that there was a truly popular Southern separatist movement before the war. That is David M. Potter, the author of the celebrated work The Impending Crisis: America Before the Civil War, 1848-1861. When the book was published, historian Thelma Jennings wrote a review for the Tennessee Historical Quarterly that both explained and gently critiqued Potter's idea:

Potter views southern nationalism as a negative phenomenon "born of resentment" to the North, and "not of a sense of separate cultural identity" (p. 469). But the two cultures were sufficiently dissimilar to turn the campaign for the protection of southern interests into a movement resembling the romantic nationalism of the age. At the time of Lincoln's election, the southern people were not united in any commitment to a southern republic nor political separatism. They were united, however, by a sense of danger, and also in a determination to defend slavery and to force the North to recognize not only their rights but their status as respectable human beings. Moreover, for southerners in general, both Unionists and secessionists, the right to secede was an article of faith.

This is kind of splitting hairs in regards to your question, though. Potter does support the idea that there was a genuine separatist movement. He just says that the cultural differences between the white North and South were exaggerated, and that the separatist movement was a minority opinion that only became (temporarily) successful due to the heat of passion following the 1860 election. Had cooler heads prevailed, many more Southerners would have stayed with the Union than would have advocated for separatism.

One historian that has partially bought into Potter's argument has been the well-respected historian of the era Michael F. Holt, author of the book on the history of the Whigs, The Rise and Fall of the American Whig Party. In 1980, he wrote a review of the aforementioned book by McCardell, published in Reviews in American History. There, Holt gives some credence to Potter's claim, but says that McCardell had mostly refuted it, yet adding that the work still has flaws because of some of its vague claims. Nevertheless, Holt seemed to be convinced that a better revision of the work would have put Potter's idea to bed.

And that may have come with the latest work on the topic:

• Shifting Grounds: Nationalism and the American South, 1848-1865 by Paul Quigley (Oxford University Press, 2011)

Once again, the work details the Southern separatist movement, starting in the aftermath of the proposed Wilmot Proviso, leading to the U.S. Civil War, and ending with the defeat of the Confederacy. Quigley's is a more modern take on the subject, accounting for the fact that the South was a "slave society," and it is difficult to underestimate how fundamentally different this made the South from the culture of the North. Rather than a single-issue political debate that could have been resolved in time, Quigley emphasizes just how much the slavery issue pervaded Southern culture and the political issues of the era. Southern identity was distinct from Northern identity, with the slavery-based hierarchy at the core.

Anyhow, the Civil War happened, and that has thrown cold water on any Southern separatist movement ever since. That's not to say that Confederate sympathizers haven't worked within the bounds of American political institutions to implement their ideologies since then, starting with the "Redeemers", a wing of the Democratic Party, mostly former Confederates who successfully implemented segregationist and white supremacy laws throughout the South. Nevertheless, the outcome of the Civil War has certainly stopped a lot of subsequent movements short of calling for separation from the United States.

One early work worth looking at is Southern Politics in State and Nation by V.O. Key (Alfred A. Knopf, 1949), which explores Southern politics from the post-Civil War era through World War II. One takeaway is that the "Solid South" was dominated by Democrats, who--at least at the federal level--would regularly oppose their own party when issues came up that defied the South's view on race. For more than fifty years after the war, their Northern counterparts were content to go along with their demands. But by the 1920s, this began to change, and by the 1940s, the pro-segregation Southerners found themselves in the minority. Famously, Strom Thurmond ran on the "States' Rights Democratic Party" ticket (a.k.a. the "Dixiecrats") in 1948, after U.S. President and fellow Democrat Harry Truman had signed Executive Order 9981, desegregating the Armed Forces.

Going further, Thurmond returned to the Democratic Party, and the Dixiecrat movement survived for a time. The "Southern Manifesto" was signed by many Southern Congressmen in 1956, but the cracks were irreparable by then. Many Southern Democrats refused to sign, including most of the delegation from Texas and Tennessee (including U.S. Sens. Lyndon Johnson and Al Gore, Sr.).

But I'm getting a bit off-topic. There have been occasional separatist movements in the South, sometimes at the state level. The Texas National Movement organization, for instance, claims over 400,000 members. And there have been countless movements in favor of "states' rights" that can be interpreted as veiled "white Southern rights" objectives. But the ghost of the U.S. Civil War has never left the American consciousness, which has likely suppressed any popularity of a "Southern separatist" party or movement.

And that leads to another reason why any such movement has failed to gain popular traction: the proposal for legal secession/separatism has quite often been part of the ideology of racist Neo-Confederate groups, such as the Abbeville Institute, the Council of Conservative Citizens, and the League of the South. It would be difficult for some political movement to advocate for Southern separatism and sincerely claim that it is not tied up in racism/Neo-Confederate ideology.

FURTHER READING:

• Dew, Charles B. Apostles of Disunion: Southern Secession Commissioners and the Causes of the Civil War. University of Virginia Press, 2001.

• Foner, Eric. Reconstruction: America's Unfinished Revolution, 1863–1877. Harper Perennial, 1988.

• Fredrickson, Kari. The Dixiecrat Revolt and the End of the Solid South, 1932-1968. UNC Press, 2001.

• Gallagher, Gary W. Becoming Confederates: Paths to a New National Loyalty. University of Georgia Press, 2013.

• Goldfield, David. Still Fighting the Civil War: The American South and Southern History. LSU Press, 2002.

• Hague, Euan, et. al (eds.). Neo-Confederacy: A Critical Introduction. University of Texas Press, 2008.

• McMillen, Neil R. The Citizens' Councils: Organized Resistance to the Second Reconstruction, 1954-64. University of Illinois Press, 1971.

• Potter, David M. and Thomas G. Manning (eds.). Nationalism And Sectionalism In America 1775-1877. Holt, Rinehart & Winston, 1949.

• Varon, Elizabeth R. Disunion: The Coming of the American Civil War 1789-1859. UNC Press, 2008.