A fascinating paper exploring the effect of partition on violence does a wonderful job illustrating how creative efforts (and rich data) can potentially dampen (though not eliminate) endogeneity concerns. In Which Side Are You On? Political Violence and Partition in Ireland 1920-1921, Elissa Berwick (MIT--Poli Sci) analyzes a quasi-natural experiment produced by the partition of Ireland in 1921. Exploiting a truly unique data set, Berwick finds that "although partition decreased violence against civilians on Northern Ireland's side of the border as compared to the Irish Free State side, violence against civilians in the border areas as a whole significantly increased."
Along with her interesting findings Berwick's research design also warrants note, especially on how it addresses endogeneity concerns. As Berwick concedes, "Partition is usually provoked by conflict, and yet its effect on conflict is the outcome of interest." Notwithstanding this tension, however, Berwick goes on to observe that:
"As for endogeneity, the initial proposal of partition came from a backbench Liberal in June 1914, years before the start of any violent civil conflict. Although the partition itself occurred in a context of civil war, its original justification was not to end conflict between northern Protestants and southern Catholics. Instead, British legislators were concerned by their inability to coerce Northern Unionists, a point driven home by the Curragh Mutiny of March 1914, in which the British Army refused to disarm the Ulster Volunteer militia. Thus the partition of Ireland was not intended to separate two sides, but instead to forestall action by a minority."
While whether Berwick's methodological optimism is warranted, of course, requires further study, her transparent and helpful discussion of the issue deserves praise.