I've heard the definition of slave society is one in which slavery is not just legal, but the entire structure of the society is based and defined around the concept of slavery and that by the 1830s the Southern states were undeniably a slave society, however do the southern states in 18th century also fit this definition? Or was it the mass profitably of cotton and vast expansion of slavery post 1800 that transformed it from a society were slavery was legal to a fully fledged slave society?
This is a pretty straightforward answer, thanks to the scholarship done by historians such as Ira Berlin and Melvin Ely. The answer to your question is an absolutely, resolutely, unambiguous-YES.
The South was without a doubt already a slave society in the 18th century. By your definition, a slave society is a society where slavery is a core component, and that cannot be separated. We already see the seeds of the system in place already in the 17th century in both the Carolinas and in Virginia.
In Virginia, the colony was meant to turn a profit, and in the absence of precious metals, and climate/topography unsuitable for sugarcane (the real moneymaker in the 17th-18th centuries), the solution was to grow tobacco. For anyone that has never grown tobacco before, it is an absolutely pain to properly cultivate, it requires lots of intensive labor and it is back-breaking. Thus slave labor was viewed as the solution to make Virginia tobacco profitable. By the 18th century, Virginia’s economy is based on tobacco, grown and cultivated by enslaved people in plantations. That is not to say that ALL of the tobacco was grown by work of enslaved people, you do see white tenant farmers growing tobacco as well, but if you want to be playing with the big boys, you own a plantation relying on enslaved people for your labor pool.
A similar situation is seen in the Carolinas, with enslaved labor from Africa being critical to the success of rice and indigo cultivation. As a matter of fact, Ira Berlin makes the case that without the experience of enslaved African individuals in cultivation of rice, the crop would have never taken off in the Carolinas in the first place.
The Virginia Slave Code of 1705 is a great example of how the institution of Slavery was already codified as a core aspect of society.
By the end of the 18th century, slavery was embedded into society in the South that even though tobacco, rice and indigo were already in economic decline, people like Thomas Jefferson and George Washington will continuously gripe that they do not know how they can end slavery. Their fortunes and plantations rely on enslaved people to run, and the irony of the American Revolution's call for Freedom on a slave society is not lost on them.
“I never mean (unless some particular circumstance should compel me to it) to possess another slave by purchase: it being among my first wishes to see some plan adopted by the legislature by which slavery in the Country may be abolished by slow, sure, & imperceptible degrees.”
George Washington 1786
Here we see GW already admit that he personally sees Slavery as a fundamental aspect of the country that must be changed, however, by a gradual phasing out of the system.
“Were it not then, that I am principled against selling negroes, as you would do cattle in the market, I would not, in twelve months from this date, be possessed of one, as a slave.”
George Washington 1794
Again, he sincerely wishes to get rid of slavery, but the very fact that he does in fact retain enslaved people at Mt. Vernon and later on during his life do show how much the Founding Fathers struggled with the institution of slavery that was so critical to their livelihood.
“There is nothing I would not sacrifice to a practicable plan of abolishing every vestige of this moral and political depravity.”
Thomas Jefferson to Thomas Cooper, September 1814
Towards the end of their lives, we do see some steps taken by them and others to gradually phase out slavery, however, the advent of the cotton gin and the profitability of cotton breathed new life into the system. The shifting towards cotton will almost single-handedly ensured that the South would continue to be a slave society into the 19th century.
Sources:
Ely, Melvin Israel on the Appotomax