It would be also very interesting to compare the North - South divide to similar divides elsewhere - industrial economy vs. the plantation-type agriculture, e.g. Northern and Southern Italy, Slovakia and the Czech lands. I've seen similar comparisons done for Latin America and Asia - basically arguing that plantation type economy with its social stratification resulted in "underdeveloped" society and types of class struggle (but references escape me at the moment).
It is problematic, however, whether such explanations would be well received by the Kultur ueber alles crowd, for whom defending popular cultural identities trumps any other consideration.
Wojtek