Eric Rauchway of Open University explains the disappearance of economic historians from history departments:
Where are the Economic Historians?, by Eric Rauchway, Open University: Darrin McMahon asks "about the fortunes of economic history and of the understanding (or not) of economics by historians." As I believe the only economist on the Open U contributor list is Lawrence Summers, whose response to this query may not come quickly, I will offer my 2 cents.
My university, UC Davis, hosts one of the best collections of economic historians in the country: Gregory Clark, Peter Lindert, Alan Olmstead, and Alan M. Taylor. I can say this without immodesty, because not one of them is in my department--the History Department--they're all economists. Nor is this atypical. Off the top of my head--this is not a comprehensive list--I can name sharp scholars of the economics of the Great Depression (Christina Romer, Brad DeLong; Ben Bernanke before he became Fed chair), nineteenth-century globalization (Jeffrey Williamson, Lance Edwin Davis), railroads (Robert Fogel), immigration and internal migration (Claudia Goldin, Joseph P. Ferrie), slavery, emancipation, and reconstruction (Fogel, Goldin, Stanley Engerman, Richard Sutch, Gavin Wright), who all work outside history departments, as indeed do most of the authors who publish in the Journal of Economic History. You can still find economic historians in history departments--Sutch's coauthor Roger L. Ransom; Robin L. Einhorn, William R. Summerhill, Niall Ferguson--but they're no longer so thick on the ground as once they were.
What happened? Partly, technical innovations in economic methods made it difficult for the untrained to understand the new economic history. ...
Economic history might have moved out of history departments for market reasons as well. If, to pursue economic history, you had to master technical skills that would make you eligible for an appointment in an economics department, you would probably prefer that to an appointment in a history department: economists get paid more because they're eligible for employment in government and business as well as universities.
Is this split a Bad Thing? Well, if traditional historians continue to keep abreast of changes in economic history relevant to their work and vice versa, so they can incorporate it into their teaching and scholarship, then it's probably okay.
I wish I could reassure Eric that economic history is alive and well within economics departments generally. I cannot, and that's a loss for our profession. I was fortunate enough to be forced to take both history of economic thought and U.S. economic history during graduate school, and face a core exam if I didn't learn them well enough, but that is no longer the case in most programs. In may cases, the courses are no longer offered at all.