Via the Freakonomics blog, this working paper by Nathan Nunn and Nancy Qian tackles a big question with an interesting design. Abstract:

This paper examines the effect of U.S. food aid on conflict in recipient countries. To establish a causal relationship, we exploit time variation in food aid caused by fluctuations in U.S. wheat production together with cross-sectional variation in a country’s tendency to receive any food aid from the United States. Our estimates show that an increase in U.S. food aid increases the incidence, onset and duration of civil conflicts in recipient countries. Our results suggest that the effects are larger for smaller scale civil conflicts. No effect is found on interstate warfare.