"My feeling is you cannot leave out the subject of slavery from the war, because slavery did affect the final outcome. Slavery was the South's albatross, economically, politically and militarily." David Upton.
George's information is not a contradiction of David. Many Southerners feared the election of Abe Lincoln with the rise of the Republican Party would result in the abolition of slavery, through the legislature without compensation to property owners. That method of ending slavery would be counter to the European method, which worked quite well. The South would have devastated economically. The many other reasons for secession are listed in the various declarations and as you pointed out, some states did not even mention slavery.
So, some leaders of the 7 "cotton states" persuaded Southern voters (white men) to choose Secession. That was not and did not mean war was imminent to Southerners or most Northerners. Some large Northern newspapers endorsed this peaceful secession.
When Lincoln provoked gunfire at Ft. Sumter and called for 75,000 volunteers to invade the South, four more states seceded in order to join the Confederacy and protect their homes and property.
By winning the war, Lincoln and his Republican regime trashed the U.S. Constitution, especially the 4th through 10th Amendments. Slavery in the Southern states was already doomed prior to the War. It would have been far cheaper in blood and treasure to compensate the owners of slaves than it was to fight this unnecessary war.