The Confederate Battle Flag was first used as a symbol of one of the armies committing treason in defence of slavery. Who themselves said that "
Our position is thoroughly identified with the institution of slavery" in their own list of causes at the time. And whose VP claimed in March 1861 that "
Our new Government is founded upon exactly the opposite ideas; its foundations are laid, its cornerstone rests, upon the great truth that the negro is not equal to the white man; that slavery, subordination to the superior race, is his natural and normal condition."
And yes, the South does get a worse rap for slavery than the rest of the US despite the presence of Sundown Towns - largely in the North. This is because, as almost everything from 1861 makes clear, the reason for the Confederacy existing
at all was to perpetuate slavery. If you look at the numbers, you find that
every single state where fewer than 24% of the population was enslaved remained loyal. And the traitors all had more than 24% of their population enslaved. Yes, it splits that cleanly. (For anyone wondering why a number of "free" states had numbers of slaves like 2 and 15, blame the
Dredd Scott decision that allowed slaveowners to take their slaves with them to the North; it is a measure of how much of a post-hoc justification the claim of States Rights was that the declarations of causes of secession normally alude to the fact that the Northern states were not happy to allow Southern Gentlemen to take their slaves to the North as one of their grievances).
So the Confederacy was created to perpetuate slavery, and it did a grand total of two notable things in its short life. Attempted to perpetuate slavery and fought an unsuccessful war.
When people fly Confederate Flags, that is the "Southern Heritage" that that flag stands directly for. I'll let
William T Thompson, the designer of the so-called Stainless Banner, the confederate flag closest to the Virginian Battle Flag normally waved explain exactly what the flag was intended to symbolise:
As a people, we are fighting to maintain the Heaven-ordained supremacy of the white man over the inferior or colored race; a white flag would thus be emblematical of our cause. … Such a flag…would soon take rank among the proudest ensigns of the nations, and be hailed by the civilized world as the white mans flag. … As a national emblem, it is significant of our higher cause, the cause of a superior race, and a higher civilization contending against ignorance, infidelity, and barbarism. Another merit in the new flag is, that it bears no resemblance to the now infamous banner of the Yankee vandals.
But this isn't where the Battle Flag's heritage ends. It wasn't particularly popular until first the Dixiecrats used it as part of their campaign to keep Jim Crow, and later George Wallace raised it in protest against the Civil Rights Act.
In short, that rag was flown at the time as part of an armed rebellion to perpetuate slavery. The official uses of it after the treasonous slaveowners were defeated have also been stunningly racist. Which means that that flag is a direct symbol of the heritage of the absolute worst of the South. Its only reason for being was to fight a war to perpetuate slavery. And its reason for popularity was racism.
And slavery was an institution that had been abolished in most of the North by the time the Civil War started in defence of slavery - modulo both the Fugitive Slave Act and the Dredd Scott decision. Which is why it is so strongly identified with the South. The Confederacy started a war to defend slavery even as those in the North had largely abolished it with their own territory - and the border states stayed with the United States.