The Census of 1860 was pretty clear about the population.
Slaveholders ruled all the states that seceded.
Most historians tell us that only a majority of South Carolinians actually favored secession.
In other states, the state legislatures made secession happen, even though a majority of the voters opposed it.
The US had 31,443,321 inhabitants. Of which 4,000,000 were slaves.
Slavery was the main cause of the Civil War. If there had been no slavery, there would have been no secession.
The Confederacy was very corrupt.