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U.S. Gun Laws and Violence in Mexico

- September 17, 2013


Yesterday’s terrible events at the Navy Yard will undoubtedly light up debates again about a possible ban on assault weapons. This issue is relevant not just in the U.S. but also south of the border where U.S. gun laws are believed to be partially responsible for increases in homicides. Some argue that this is just a convenient scapegoat but there is some solid social science evidence that the 2004 expiration of the U.S. Federal Assault Weapons Ban did have an effect on homicides in Mexico.

One paper I blogged about before, by  Arindrajit Dube (UMass)Oeindrila Dube (NYU) and Omar Garcia Ponce (NYU), is now the lead article (ungated for now, I believe) in the  American Political Science Review, the premier academic journal in political science. The graph above displays some of the evidence: homicides increased more in areas close to U.S. states that did not have a pre-existing ban than in California, which upheld its prior ban on assault weapons. The abstract is below:

To what extent, and under what conditions, does access to arms fuel violent crime? To answer this question, we exploit a unique natural experiment: the 2004 expiration of the U.S. Federal Assault Weapons Ban exerted a spillover on gun supply in Mexican municipios near Texas, Arizona, and New Mexico, but not near California, which retained a pre-existing state-level ban. We find first that Mexican municipios located closer to the non-California border states experienced differential increases in homicides, gun-related homicides, and crime gun seizures after 2004. Second, the magnitude of this effect is contingent on political factors related to Mexico’s democratic transition. Killings increased disproportionately in municipios where local elections had become more competitive prior to 2004, with the largest differentials emerging in high narco-trafficking areas. Our findings suggest that competition undermined informal agreements between drug cartels and entrenched local governments, highlighting the role of political conditions in mediating the gun-crime relationship.

One may doubt that the plausible externalities of U.S. gun laws will be taken seriously in policy debates. That is probably so but this is a major issue among immigrants from Central America (not just Mexico). Hispanics are overwhelmingly supportive of stronger gun laws and we keep hearing that they are an important demographic.