Last week, International Studies Quarterly published a study by Matthew Krain, an Associate Professor of Political Science at the College of Wooster, examining "the effectiveness of military action on the severity of ongoing instances of genocide and polititcide."
According to the press release
The study reveals that only overt military interventions that explicitly challenge the perpetrator appear to be effective in reducing the severity of the brutal policies. Military support for targets, or in opposition to the perpetrators, alters the almost complete vulnerability of unarmed civilian targets. And these interventions that directly target the perpetrators were not, on the whole, found to make matters worse for those being attacked ... He finds that even military intervention against the perpetrator by a single country or international organization has a measurable effect in the "typical" case.In the introduction to the study, Krain notes
When a single international actor challenges the aggressor, the probability that the killings will escalate drops while the probability that the killings will decrease jumps. Each additional intervention by another international actor raises the chance of saving lives.
Policy makers faced with situations like those in Rwanda or Bosnia, Kosovo or Darfur, are forced to rely on past experience with interventions in other types of internal conflicts, often with disastrous results. This study is a step toward a better understanding of the effectiveness of potential responses by the international community to genocides and politicides.Krain goes on to examine various intervention methods of dealing with on-going genocides and politicides (the "impartial intervention model," the "witness model," the "bystander model," etc...) and notes that not one of them is capable of reducing the severity of such situations.
After conducting a statistical analysis of the various models, Krain concludes
Policy maker concerns that intervention on the behalf of target populations will escalate the killing appear to be unfounded.He then discusses his finding as they relate to Darfur, writing
The only overt military interventions that appear to be effective in reducing the severity of genocides or politicides are those that explicitly challenge the perpetrator
Intervention against the Sudanese government and the Janjaweed within the first year of the genocide would likely have had a measurable effect on the severity  of state-sponsored mass murder in the following year.Kraine does not claim that military intervention is the "only" option. In fact, he notes that "policy makers have a range of options available to them in the face of an ongoing genocide or politicide" and that his study "only examines one of those options."
Keeping that in mind, it is hard to argue with Kraine's basic conclusion
If actors wish to slow or stop the killing in an ongoing instance of state-sponsored mass murder, they are more likely to be effective if they oppose the perpetrators of the brutal policy.