Answer:
The minority that had the greatest political power in its region in the period before the civil war was "planter in the south".
Step-by-step explanation:
To understand this answer we have to analyze the context first, so:
In the first place, there were more millionaires per capita in the Mississippi river valley in 1860 than anywhere else in the United States of America. Second, the elite master class of the south created their own culture and social rules. Making arguments to convince ignorant people that what they said was the truth. Third, by having the power they were able to create and define the political circles in the south. Gaining political weight that supported them and their ideas. The cotton boom allowed them to gain more money to keep the power.