Correct and anyone who doubts that should read the South Carolina Secession Declaration where slavery is specifically mentioned eighteen times.
From a constitutional standpoint, the Confederacy's problem was that it never addressed the Articles of Confederation which speaks of a PERPETUAL Union, a Union that the Constitution sought to make "more perfect."
Wagglebee, the Articles of Confederation were superceded by the Constitution. The fact that the AoC speak of a perpetual union is immaterial to what Constitutional rights the South had in secession.
South Carolina Ordinance Of Secession
AN ORDINANCE to dissolve the union between the State of South Carolina and other States united with her under the compact entitled “The Constitution of the United States of America.”
We, the people of the State of South Carolina, in convention assembled, do declare and ordain, and it is hereby declared and ordained, That the ordinance adopted by us in convention on the twenty-third day of May, in the year of our Lord one thousand seven hundred and eighty-eight, whereby the Constitution of the United States of America was ratified, and also all acts and parts of acts of the General Assembly of this State ratifying amendments of the said Constitution, are hereby repealed; and that the union now subsisting between South Carolina and other States, under the name of the “United States of America,” is hereby dissolved.
Done at Charleston the twentieth day of December, in the year of our Lord one thousand eight hundred and sixty.