The South is the subject of a dissertation (6)
I believe the answer is:
thesis
'subject of a dissertation' is the definition.
'thesis' can be an answer for 'dissertation' (synonyms). I'm not sure about the 'subject of a' bit.
'the south is' is the wordplay.
'south' becomes 's' (abbreviation).
'the'+'s'+'is'='THESIS'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for thesis that I've seen before include "Treatise advancing a new point of view resulting from research" , "Proposition" , "research paper" , "A lengthy essay, perhaps for degree" , "Long research essay or treatise written for university degree" .)