Genocides and mass killings are still part of modern history, and when they happen it is most of the time too late to intervene. Thus prevention is more effective, but one needs to identify where there are risks.
By looking at past history with some good use of theory, Joan Esteban, Massimo Morelli and Dominic Rohner identify the following criteria: 1) large natural resources, 2) rents distributed proportionally, 3) low productivity, and 4) weak state. And a civil war can help, too.
Of particular interest here is the impact of constitutional constraints that force a government to provide resources to some groups according to their number. While such constraints may be well meant, to reduce disparities, they have the adverse effect of providing incentives to reduce the group size, by mass killing or displacement. In other words, provisions that are supposed to protect minorities may end up eradicating them.