Let’s have a closer look at that, and see where it takes us.
Plantation owners had a huge investment in slaves, so they wanted productive slaves, not unproductive slaves. That meant finding the most profitable balance between resources spent keeping slaves alive, healthy and productive, verses replacing unproductive or dead slaves. The blocking of the Atlantic slave trade by England, other European nations and the USA would have had the effect of forcing plantation owners to make better efforts at keeping their slaves productive rather than simply replacing them as they had previously been able to do. Slaves cost money to import, but they also cost money to keep alive. For example, Caribbean sugar plantation slave life expectancy was seven years in the late 17th century (Blackburn: The Making of New World Slavery, p. 339), and at one of my family’s plantations in northern South America’s Demerara, the life expectancy was three years (sorry, I can’t recall the text – dig about on the 1823 slave rebellion there and you’ll come across the general brutal conditions as well as the atrocities). Now ask yourself how cessation of the Atlantic slave trade would make a plantation owner feel? Frustrated at the increasing cost of disposable labour, and pissed of at the English, other Europeans, and the USA federal government that were strangling the supply of slaves.
So there we have the civilized world conspiring to put the screws to slavery. Now let’s have a look at the timing of the USA federal government’s opposition to slavery.
1776-1783: revolution and formation of the USA resulting in the Treaty of Paris, and among other things, a nice sounding USA government document that goes on about freedom (although not freedom for slaves).
1787: USA’s Northwest Ordinance that banned slavery north of the Ohio and set the stage for the future growth of the USA.
1794: USA’s Slave Trade Act that prohibited the building or outfitting of slave ships.
1807: importation of slaves banned by the USA, the slave trade banned by Britain. Britain establishing the West African Squadron to suppress the Atlantic Slave trade.
1820: USA starts sending ships to fight along side of the West African Squadron.
1842: USA formalizes its involvement with the West African Squadron though the Webster–Ashburton Treaty.
Quite simply, the USA federal government, all the way back to Jefferson, pushed to strangle slavery, to the detriment of the slave states where plantation owners had for generations relied on slaves.
In that context, yes, the issue of states’ rights – specifically states’ rights to have and profit from slavery – is a valid point, for from the slave states’ way of looking at things, slavery was at the core of their economy and society, and the USA government was impinging on their right to maintain their economy and society.
Basically, the sons of bitches were entrenched racists who put their own interest above human rights, so while the civilized world, including the USA government, moved forward over the decades to reduce and end slavery, the slave states literally fought tooth and nail to maintain their traditional “right” to slavery.
Claiming that the American civil war was about states’ rights rather than slavery ignores the glaringly obvious fact that it was the right to have slaves and the right to obtain slaves that were the rights the slave states were fighting for. When it comes to slave states and their cultural descendants, states’ rights and the right to have and obtain slaves are inextricably intertwined.