Confederate only.
I know that many on both sides of the issue try to use the Founders as a "gotcha" point, but historically it doesn't really pan out. The reason being that history shows us through letters, diaries and little-known speeches and articles of quite a few of the Founders who were slave owners were very conflicted over fighting for freedom and creating a government that still kept slavery as an institution.
The southern colonies that became states were called the Southern Block. And according to the Constitutional Convention notes, they made it very clear that if slavery were abolished as slave owners like Washington and Jefferson wanted..then the Southern Block would walk away and form their own nation. At the time, the US Army was not strong enough to hold the Southern Block in by force, so Washington conceded to not even discuss the issue anymore. But men like Washington often manumitted their salves upon death. They wrote about the plight of slaves and often railed at their own failures to not find a better way to free them.
Over time, more and more people in the northern states became abolitionists, or at least anti-slavery and voted accordingly.To the point that anti-slavery laws were passed that the Southern Block hated. The nation was on its way to abolish slavery (still not equal mind you, but definitely ending slavery). Soon, you had a number of states that supported slavery and those that did not. Then the 1850 Compromise came into being and arguably made things worse.
Finally, Lincoln was elected and crap boiled over. There were multiple reasons for the Civil War, certainly, but of the big reasons, slavery was one of them. The states that made up the original Southern Block would be the states that made up the Confederacy as well as the new states that came in as slave states under the 1850 Compromise. They never wanted to get rid of the slaves to begin with...and as part of the reason to secede, they tried to make a new nation whose Constitution enshrined slaver and demanded its protection. Then they created armies, went to war and killed their fellow Americans over that and other issues.
Washington, Jefferson and others who held slaves actively tried to find ways to get rid of slaves in a peaceful and legal fashion...they just failed. But they tried. The CSA came from states that never wanted to and even threatened war when making the Constitution over it. And then they did use war to keep it.
That's why.