Which events played the greatest role in creating these conditions in the south during the antebellum era?

was it the northwest ordinance of 1789

The correct answer of the given question above would be THE INVENTION OF THE COTTON GIN. The event that played the greatest role in creating these conditions in the south during the Antebellum era is the invention of the cotton gin. Other choices of the given question that you might have missed are the northwest ordinance, secession of South Carolina, and Dred Scott case. Hope this answer helps.