Brion McClanahan makes a good point here.
The Confederacy never had its own Declaration of Independence. There wasn’t any need for one for two reasons.
First, the original version only acknowledged the fact that the American colonies were already effectively independent states. Virginia’s royal governor Lord Dunmore had fled the state on June 8, 1775 over a year before the Declaration of Independence. British rule in Virginia had been collapsing for two years before the Declaration of Independence. Virginians seized their own independence.
Second, the assumption was that we were already free and independent states as this had been established by the American Revolution. This is what we had fought for in the Revolution. It was acknowledged by Great Britain in the Treaty of Paris in 1783. The power to join the Union is the power to leave it. We left the Articles of Confederation and each state had to ratify the U.S. Constitution.
Note: The establishment court historian Allen Guelzo has a new book out on Robert E. Lee.