The key words would be "the new converts," not the whole of the Confederate constitutional convention or government. Whether "new converts" is more accurate than "moderates" or "cooperationists" is another matter, but they were latecomers to the secessionist cause, in contrast to those who had been for secession for some time and who had originally sparked secession in the Deep South.
George Rable writes in "The Confederate Republic":
On March 8, Tom Cobb moved to prohibit the admission of nonslaveholding states to the Southern republic. But Cobb's own Georgia delegation was divided, with Stephens and Robert Toombs leading the opposition. After three days of debate the motion failed. The delegates eventually agreed to a compromise allowing for the admission of free states but requiring a two-thirds vote of approval from both House and Senate. This result gave new life to reports of sentiments for compromise in the convention and greatly alarmed the fire-eaters. Both sides probably attached too much importance to this matter because it was unlikely that any free states would want to join the Confederacy, and in any case, the new nation's commitment to slavery was embedded in the Constitution.
The convention was in a compromising mood and the measure wasn't as significant as some late 20th century historians might have believed. 2/3rds of each half of the Confederate Congress would have to approve and the Senate would vote as states.
This meant that the Deep South States would be able to block any admission of free states on the first go around. The 2/3rds requirement and the Confederacy's explicit and pronounced committment to slavery meant that few free states would realistically be tempted to join.
Why would free states that had objected to slave catchers coming north to take back runaways ever vote to join a country that was even more dedicated to catching and returning runaways? Why would Deep South militants who were worried about the flagging committment to slavery in the Border States and even in the Upper South agree to admitting free states into their Confederacy? That would be inviting the abolitionist foxes into the slaveowner's henhouse. So yes, the door was theoretically open to admitting free states, but it was based on some imaginary future. It was also a good public relations measure, if anyone had noticed it at the time.
Emory Thomas suggests in "The Confederate Nation" that some moderates believed that free states in the Mississipi Valley might at some point be tempted to join, and that those states' admission would strengthen the Confederacy to get territories for slave owners elsewhere -- in the West, in Mexico or (I'll add) the Caribbean. In any event, none of this affected the Confederacy's committment to slavery, whatever late 20th century historians might imagine.
Politicians make compromises and concessions. They kick the can down the road. Often they make sure that their concessions aren't likely to have serious real world consequences. The Confederate convention didn't bar the admission of free states. They didn't make it easy either. If it happened at some point down the road, the CSA would deal with that later. It didn't affect the Confederacy's commitment to slavery.
There's a parallel to the Corwin Amendment. Congress and Lincoln threw it out there as a last ditch attempt to save the union. It worked for a minute. The Upper South rejected secession before war began. Then it didn't work. It was never really going to bring back the Deep South States that had seceded. Secession gave them all the security for slaveholding they wanted. They had crossed the Rubicon and they weren't coming back.
It isn't true that Lincoln was lobbying the states to ratify the amendment after war began. The amendment had already failed in its purpose, and there was no reason to carry on with it. Even before the war, Lincoln's support for the amendment was lukewarm and distanced. He said he had no objection to it and notified state governors that the amendment was submitted for ratification without explicitly endorsing it.
Be they "new converts" or not, their will obviously represented the majority since their proposal to ban the slave trade was passed and the attempt to prevent states that did not allow slavery from joining the Confederacy was defeated.
George Rable writes in "The Confederate Republic": On March 8, Tom Cobb moved to prohibit the admission of nonslaveholding states to the Southern republic. But Cobb's own Georgia delegation was divided, with Stephens and Robert Toombs leading the opposition. After three days of debate the motion failed. The delegates eventually agreed to a compromise allowing for the admission of free states but requiring a two-thirds vote of approval from both House and Senate. This result gave new life to reports of sentiments for compromise in the convention and greatly alarmed the fire-eaters. Both sides probably attached too much importance to this matter because it was unlikely that any free states would want to join the Confederacy, and in any case, the new nation's commitment to slavery was embedded in the Constitution.
It showed that far from being "all about" slavery, the CSA was perfectly willing to admit states that had banned it and that they were more concerned with having a more decentralized form of government and fully respecting the sovereignty of the states. The Confederate Constitution no more had slavery embedded in it than the US Constitution did. The situation wrt slaves, the states' laws and the rights of slaveholders were not different than had been the case in the US.
The convention was in a compromising mood and the measure wasn't as significant as some late 20th century historians might have believed. 2/3rds of each half of the Confederate Congress would have to approve and the Senate would vote as states.
The CSA was in general much more willing to respect the sovereignty of the states and had a much more decentralized government. That was true of everything - not just the admission of new confederate states.
This meant that the Deep South States would be able to block any admission of free states on the first go around. The 2/3rds requirement and the Confederacy's explicit and pronounced committment to slavery meant that few free states would realistically be tempted to join.
I don't agree with that assessment at all. If a state that had already banned slavery wanted to join and the states in the Confederacy deemed them a trustworthy partner as well as a beneficial new member to have, they would have almost certainly been admitted.
Why would free states that had objected to slave catchers coming north to take back runaways ever vote to join a country that was even more dedicated to catching and returning runaways?
Some states saw considerable opposition to slave catchers capturing fugitive slaves. Others not nearly so much. I doubt the ones that had strong movements against it would have ever considered joining the CSA anyway so its a moot point.
Why would Deep South militants who were worried about the flagging committment to slavery in the Border States and even in the Upper South agree to admitting free states into their Confederacy?
I haven't seen evidence of some deep worry on the part of Southerners from the Deep South that the states of the Upper South had "a flagging commitment to slavery". Southerners viewed it as a matter for the people of each state to decide.
That would be inviting the abolitionist foxes into the slaveowner's henhouse.
Just because the people of one state had chosen to get rid of slavery it does not necessarily follow that they would then try to force their choice on others. Most Southerners saw it as a matter for each sovereign state to decide.
So yes, the door was theoretically open to admitting free states, but it was based on some imaginary future. It was also a good public relations measure, if anyone had noticed it at the time.
Nobody could know what the future would hold. The future is always imaginary.
Emory Thomas suggests in "The Confederate Nation" that some moderates believed that free states in the Mississipi Valley might at some point be tempted to join, and that those states' admission would strengthen the Confederacy to get territories for slave owners elsewhere -- in the West, in Mexico or (I'll add) the Caribbean. In any event, none of this affected the Confederacy's committment to slavery, whatever late 20th century historians might imagine.
Slavery was primarily used in the production of cotton and tobacco - and to a much lesser extent, rice and sugar. The West is simply not suitable for these crops. Witness the tiny number of slaves actually domiciled in the Arizona Territory which included present day New Mexico as well. What the Confederacy was really committed to was respecting the sovereignty of each state.
Politicians make compromises and concessions. They kick the can down the road. Often they make sure that their concessions aren't likely to have serious real world consequences. The Confederate convention didn't bar the admission of free states. They didn't make it easy either. If it happened at some point down the road, the CSA would deal with that later. It didn't affect the Confederacy's commitment to slavery.
The Confederacy was no more committed to slavery than the US was.
There's a parallel to the Corwin Amendment. Congress and Lincoln threw it out there as a last ditch attempt to save the union. It worked for a minute. The Upper South rejected secession before war began. Then it didn't work.
The states of the Upper South chose to stay in initially not because of the Corwin Amendment which wasn't drafted until after the 7 states of the Deep South had already seceded. The states of the Upper South only chose secession when they were forced to choose between that or attacking other sovereign states to impose a government on them that they did not consent to. The fact that the North was perfectly willing to explicitly protect slavery effectively forever demonstrates once again that slavery was not really threatened in the US.
It was never really going to bring back the Deep South States that had seceded. Secession gave them all the security for slaveholding they wanted. They had crossed the Rubicon and they weren't coming back.
The hope was precisely that it would bring back the states of the Deep South. Since slavery wasn't really their primary concern - and wasn't threatened in the US anyway - it did not address their big concerns which were economic and philosophical against the ever growing usurpation of more and more power by the federal government at the expense of the states. Refusing the Corwin amendment which they had to know would bring war was the one thing that did risk the continuing existence of slavery. They chose that course because slavery was not their main concern.
It isn't true that Lincoln was lobbying the states to ratify the amendment after war began. The amendment had already failed in its purpose, and there was no reason to carry on with it. Even before the war, Lincoln's support for the amendment was lukewarm and distanced. He said he had no objection to it and notified state governors that the amendment was submitted for ratification without explicitly endorsing it.
He didn't put nearly the effort into getting states to ratify it after he started the war that he had before that. Still, he did continue to exert influence to get it passed. While he claimed he merely "had no objection" to it and even that he had not seen it in his inaugural address, that was a lie. He had orchestrated its passage and had worked closely with Corwin and Seward to draft it, get it passed with a supermajority in both houses of Congress and then lobby state governments to pass it. Politicians lied then just as they do today.