From a preliminary report by Oeindrila Dube and Suresh Naidu Bases, Bullets and Ballots: the Effect of Military Aid on Political Conflict in Columbia (via Chris Blattman Your aid dollars at work… suppressing voters):
"The findings suggest that foreign military aid may strengthen the capacity of non-state armed actors, undermining domestic political institutions". They suggest that the paper has clear policy implications in giving military aid to countries where there are informal connections between the armed forces and illegal armed groups and briefly discuss the cases of Iraq, East Timor and Mexico.
More papers by Suresh Naidu and colloborators are available here and Oeindrila Dube's profile here
Another paper by Arindrajit Dube, Naidu and Ethan Kaplan Coups, Corporations, and Classified Information is reported in Slate They Made a Killing:
"With a U.S. puppet back in the president's mansion, UFC's profits were safe. But it appears the company wasn't the only beneficiary of this Cold War cloak-and-dagger diplomacy: A recent study by economists Arindrajit Dube, Ethan Kaplan, and Suresh Naidu argues that those in on the planning process also profited handsomely. By tracking the stock prices of UFC and other politically vulnerable firms in the months leading up to CIA-staged coups in Guatemala, Chile, Cuba, and Iran, the researchers provide evidence that someone—perhaps one of the Dulleses, Cabots, or others in the know—was trading stocks based on classified information of these coups-in-the-making."
P.S Further discussion between Andrew Gellman and the authors in The effects of U.S. military aid on political violence in Colombia: a back-and-forth regarding the strength of the causal evidence.