This won’t come as a shock to anyone, but the NY Times reports that diplomatic (also military, constitutional) history is declining and has been replaced by cultural history, women, minorities, immigrants, etc. Sample:
"How have some departments sliced up the pie? At the University of Wisconsin, Madison, out of the 45 history faculty members listed (many with overlapping interests), one includes diplomatic history as a specialty, one other lists American foreign policy; 13 name either gender, race or ethnicity. Of the 12 American-history professors at Brown University, the single specialist in United States empire also lists political and cultural history as areas of interest. The department’s professor of international studies focuses on victims of genocide."