"The American Civil War wasn't about slavery because slavery didn't actually exist in the South"

[Andy_L]

A previous answer to that very question

Did anyone advocate for a new Constitution, c. 1865 (in the US, if I wasn't clear)?

By 1860 only the balance in Senate counted. Northern population growth had overwhelmed the South; there was a 70/30 split in 1860, out of a population of 31 million. The South had around 4 million slaves, so they would have gained 1,500,000 extra in the Census, or about 5% of the total population, hardly enough to change the balance in the House. The 1870 census showed a population of about 38 million, making the free black population an even smaller proportion of the growing country.