Southern Exceptionalism in American Political Science
This isn't a theory of political science, there's just an awful history in American political science for treating the U.S. south as something 'exceptional' or 'different'. And I don't mean 'controlling for geographical region in a regression'. I mean 'observations are categorically excluded from analysis'.
Reading Notes
Ideological Realignment and Active Partisans in the American Electorate, Alan I. Abramowitz and Kyle L. Saunders, 2004
To be fair, the authors didn't exclude data. But they did regress on an indicator variable as 'south'/'not south', erasing all of the other geographic predictors of variation.