Here’s a link to the various Ordinances of Secession.
http://www.civil-war.net/pages/ordinances_secession.asp
To the extent that the states went on record to state a particular grievance identifying the specific state’s right that was being abrogated, with one exception it was slavery. The one exception was Missouri, which claimed it had been invaded by a hostile federal army. Texas threw in some comment about not securing the southern border, but the chief complaint there was slavery.
To those who say that the Civil War was about “state’s rights” and not specifically about slavery, they should read what the state’s own legislators said about why they were committing acts of rebellion and insurrection.
It was crystal clear to the leadership what they were fighting for. It was to avoid what would be the largest sudden loss of wealth in the history of the Republic. Thinking may have been a bit more confused among the ranks in the army who were not slaveholders.
Slave-state Missouri was majority pro-Union and never voted to secede.
Missourians served in the Union army over 3-1 versus Confederates.
In October 1861 a rump-assembly of 39 Missouri House and 10 Senate members declared secession and Neosho their capital.
Accepted as the 12th Confederate state, the rump-government was pushed out of Missouri by end of 1861, Confederate Governor Jackson died in 1862 and Marshall, Texas became the Confederates' capital in exile of Missouri.
Bottom line: like Kentucky, Maryland & Delaware, Missouri was a Border slave-state but majority Unionists, on the order of two or three to one.
No majority ever voted to secede and rump-elements which did were never considered legitimate by their own states' citizens.