I'm sure you intended to say here: every 1st round secession document which gave reasons listed slavery most prominently.
Not every secession document gave reasons, so not every document listed slavery.
Here is a summary of six 1st Round "Reasons for Secession" documents
Note: the first four are official "Reasons for Secession" by South Carolina, Mississippi, Georgia and Texas, the only 1st Round states which issued reasons.
1st Round states of Florida, Louisiana & Alabama did not produce "Reasons for Secession" documents.
I'm including Robert Rhett because he wrote at the same time as South Carolina's secession to encourage other slave-states to secede.
CSA Vice President Alexander Stephens's words are the notorious "Cornerstone Speech".:
| Reasons for Secession | S. Carolina | Mississippi | Georgia | Texas | Rbt. Rhett | A. Stephens | AVERAGE OF 6 |
|---|---|---|---|---|---|---|---|
| Historical context | 41% | 20% | 23% | 21% | 20% | 20% | 24% |
| Slavery | 20% | 73% | 56% | 54% | 35% | 50% | 48% |
| States' Rights | 37% | 3% | 4% | 15% | 15% | 10% | 14% |
| Lincoln's election | 2% | 4% | 4% | 4% | 5% | 0% | 3% |
| Economic issues** | 0 | 0 | 15% | 0% | 25% | 20% | 10% |
| Military protection | 0 | 0 | 0 | 6% | 0% | 0% | 1% |
** Economic issues includes tariffs, "fishing smacks" and alleged favortism to Northerners in Federal spending.
Bottom line: across six documents, slavery accounted for 48% of the words explaining why they seceded.
No other issue came even close.
It's also important to notice that eight Upper South and Border States refused to secede so long as slavery was the only real reason.
Then after Fort Sumter four of those states declared secession based on Virginia's claim of "injury or oppression", not slavery.
Your labels, first round and second, etc. are misleading at minimum.
there were a total of 11 state legislatures or conventions, 1 rump state convention, 1 territorial convention, and 2 Indian tribes that published one or more secession documents around the beginning of the war.
If taken altogether, they published at least 20 documents declaring or otherwise affirming their secession. 11 were ordinances officiating the secession act itself adopted by the 11 state conventions, legislatures, or popular referendum. The conventions of 4 of those 11 states adopted an additional “Declaration of Causes” as a nonbinding legislative resolution, and serving as public information only and not legally binding on anything.
With regard to the official documents of secession, none of the original 7 and eventual 11 ordinances mentioned slavery as a cause of their decision to leave the Union.
The convention of South Carolina also adopted a letter of causes addressed to all the other southern states outlining their list of justifications and urging others to join them. This document is the same type of narrative offered by other states. It is interesting reading but nothing more than ancillary composition.
Out of the 20 total declarations, ordinances, and other secession documents only 6 mentioned slavery in any context beyond geographical nomenclature (only 5 mention it at any length - the sixth is in a single brief clause).
Fourteen of those documents specify other causes, either in addition to slavery or without mentioning it at all.
As noted, and let us get it straight this time, the Official original 7 do not list any causes.
Georgia Secession Decree (January, 1861):
“(The Northern States) have endeavored to weaken our security, to disturb our domestic peace and tranquility, and refused to comply with their constitutional obligations to us in reference to our property, and by the use of their power in the Federal Government have striven to deprive us of an equal enjoyment of the common Territories of the Republic.
“The people of Georgia, after a full and fair and deliberate hearing of the case, have declared with firmness that (the Northern States) shall not rule over them.”
Mississippi Secession Decree (January, 1861):
“(The North) has given indubitable evidence of its design to ruin our agriculture, to prostrate our industrial pursuits and to destroy our social system.
“Utter subjugation awaits us in the Union, if we should consent longer to remain in it. It is not a matter of choice, but of necessity (to secede).”
Texas Secession Decree (February, 1861)
“The controlling majority of the Federal Government, under various pretences and disguises, has so administered the same as to exclude the citizens of the Southern States, unless under odious and unconstitutional restrictions, from all the immense territory owned in common by all the States on the Pacific Ocean, for the avowed purpose of acquiring sufficient power in the common government to use it as a means of destroying the institutions of Texas and her sister slaveholding States.”
Louisiana Secession Decree (January, 1861):
“The people of Louisiana are unwilling to endanger their liberties and property by submission to the despotism of a single tyrant, or the canting tyranny of pharisaical majorities (in the North).”
Mississippi Secession Decree (January, 1861): “That they have elected a majority of electors for President and Vice-President on the ground that there exists an irreconcilable conflict between the two sections of the Confederacy in reference to their respective systems of labor and in pursuance of their hostility to us and our institutions, thus declaring to the civilized world that the powers of this government are to be used for the dishonor and overthrow of the Southern section of this great Confederacy.”