'Sections' is the usual term for before the war, although 'regions' also works.

During the war, though, it really should be 'nations', though some people shy away from that. Sectional identify from before the war quickly became national identity, and the Confederacy exercised all the prerogatives of a sovereign state; indeed, the nation-state there was more advanced than in the U.S., with the Confederate government arrogating more and more power to itself in its desperation to survive and win the war.

While Unionists had been a handy majority throughout the south before the war, even in the runup to the Fort Sumter crisis and Lincoln's call for volunteers, southerners became ardent Confederates with astonishing speed once the shooting started, though of course many didn't even wait that long and Kentucky became a Confederate state after the war.

Ultimately, the loyalty of much of the South to the Union was conditional on its protection of slavery. The anti secessionist majorities elected to the Virginia secession convention were not anti-slavery. The speakers at the convention were very frank; they were deciding which of the two ways -the U.S. or the Confederacy- would better protect slavery. It was absolutely the most important thing to them, the common denominator in arguments for and against secession. There's a great database where you can search the transcripts of the conventions, and you can chart the delegates mentioning slavery more than ever before at the moment of secession.

Because of the pervasive power of pro-slavery ideology, as well as the fact that it really was the 'greatest material interest of the world', a new nation explicitly devoted to the institution of slavery had a powerful appeal. Gary Gallagher uses General Ramseur as an example; he was a fierce advocate of slavery, and during the war, his pride in his North Carolina origins largely depended on the state's perceived support for the slave confederacy. He'd always disliked the Yankees, but this deepened into loathing and hatred over the course of the war. He demanded everything be subordinated to the needs of the new nation, be it individual or states' rights.

I've already written a nice long post about Robert E. Lee and Confederate nationalism here; could always use the extra karma. Suffice to say, despite a lifetime of loyal service in the U.S. Army, Lee not only fought to establish a separate nation, but remained a Confederate nationalist even after the surrender at Appomattox.

Despite all attempts to find a compromise, war came, and sectional dislike hardened into national hatred. Prewar stereotypes of northerners -'bigoted Puritans and tightfisted Yankees', 'vagabonds from Ireland and Germany'- informed the Southern view of the conflict; they lamented that every man of theirs who fell on the battlefield would be a valuable citizen lost, but that the dregs of society the U.S. sent to their deaths would be a net gain for them.

Mere weeks into the conflict, when T.J. Jackson arrived in the Valley to take command of the regiments raised for Confederate service, he asked the men of Augusta county, who had repeatedly voted in Unionist delegates for the Secession Convention, whether they would enlist for one year or for the entire war; 'For the war! For the war!' they shouted together. Over 3,000 men in this formerly Unionist county had voted for secession when the time came for popular vote ratification, but only ten cast their votes for the old Union.

Southern Christianity provided a powerful justification for secession and war, and the people of the new Confederate nation intensified their pre-war religious interpretation of sectional conflict. The South always believed itself more faithful to God than the North, believing in a literal interpretation of the Old Testament (pointing out that the Bible never explicitly says that slavery is wrong, and does not present ancient slavery as in any way wrong). They furthermore identified not only slavery in general, but the inferiority of black people as the will of God; in the infamous 'Cornerstone Speech', Alexander Stephens claimed that the superiority of the white man is so manifestly evident as the will of God that regardless of constitutional rights, he would leave any government that did not acknowledge it, and that explicitly founding a new nation on the principle of white supremacy made it superior to any previous nation, for instead of human ideology, it rested on an immutable law of nature, the manifest will of God. Confederates took heart in the fact that the men leading them to independence -Lee, Stonewall Jackson- were pious Christians, and religious revivals swept through army camps, especially in 1862-3. They saw their new Confederacy as 'God's republic', resting on the manifest truth of inequality rather than the U.S.'s invented equality.

The Confederates drew on a wide range of justifications for the sacrifice of its citizens. Edward Ayers describes one handbill encouraging enlistment in the Confederate army from the first month of the war, which decried the 'abolitionist hordes' polluting the state, and urged Virginia men to take up Patrick Henry's demand of 'Liberty or Death!' in defense of home and hearth, to aid their brothers already in the field, and to protect the graves of their ancestors.

As previously alluded, they drew heavily on the legacy of the American Revolution; it's not a coincidence that the capital of the Confederacy was in Richmond, and that the city's statue of George Washington is front and center on the Great Seal of the Confederacy. To them, the case for a Confederate George Washington was the most obvious thing in the world. When the U.S. accused them of betraying the Founding Fathers, they explicitly identified Washington as 'a rebel and a slaveholder', as if to ask, 'which one of is is really out of step with the founders?' Light Horse Harry Lee's own son was leading the main Confederate army into battle, and he had even married into George Washington's (adopted) family; it was even common to call Union troops 'Hessians', after the German soldiers used to bolster the British forces during the Revolution.

The battlefield is the ultimate testament to Confederate nationalism. Outnumbered four to one in terms of white population by the U.S., the Confederacy fought for four long years, bolstering the latent Confederate nationalism of its citizens with its victories. Even when the main Union army was closing in on Richmond in 1862, the people stayed loyal to their nation and to the fight, and in doing so, they signed a death warrant for their domestic institution should they fail. That year, the Confederate government had enacted the first conscription law in American history, and all told, about 1/5 white southerners fought for the Confederacy. In Virginia, that meant 94% of the state's white men of military age (16-55), and Virginia wasn't even the most heavily mobilized state.

The Confederacy fought on despite devastating defeats and threats of destruction; the war ended when the Confederate field armies were decisively beaten, and no sooner. Lee wrote in January 1863 that Lincoln's emancipation policy left them 'no choice but victory or degradation worse than death.' When Sherman marched through Georgia and the Carolinas almost unopposed, hamfisted tales of Yankee atrocities strengthened Confederate resolve; they would not, they could not yield to an enemy that did the things Sherman did.

In the Shenandoah, national resolve held even after multiple rounds of devastation by passing armies; they poured scorn on Grant's alleged cowardice, supposing he was tired of fighting Lee's veterans, instead turning his arms against women and children. To them, the Yankee had become a barbarian, even a demon, and they yearned for the chance to retaliate in kind. The newspapers urged the people of the Valley to give everything they had for the army and the national struggle for independence, and even after Lee's surrender following four years of devastation, one woman claimed she was willing to fight for four more years if they could win their independence.

The Army of Mississippi was besieged in Vicksburg and capitulated; the Army of Tennessee was vanquished in its deathride to Nashville, and the Army of Northern Virginia was encircled when it finally evacuated its defenses of the capital after nearly a year of siege. For his part, Lee accepted the verdict of the battlefield, and believed that the only honorable course of action following their nation's utter defeat was to submit to the U.S. again; he applied for a pardon and sought to have his citizenship status restored, though a bureaucratic mixup meant the forms were separated. However, despite outward acceptance of the verdict of the battlefield, the lingering post-war allegiance to the Confederacy demonstrates the centrality of Confederate nationalism during the war.