(Carlos Jasso/AP Photo)
(Carlos Jasso/AP Photo)

American debates over gun control are messy. On the one hand, New York Times columnist David Brooks argues that gun control laws like the Federal Assault Weapons Ban had no real effect. On the other, Adam Gopnik at the New Yorker argues that the correlation between gun laws and gun violence tells us that gun control works. Pundits can disagree because it is hard to figure out what is causing what. For example, it might be difficult to know looser gun regulation causes violent crime (criminals might find it easier to buy guns) or violent crime causes looser gun regulation (as people who are frightened by high crime rates look for changes in the law so that they can buy guns to protect themselves). Both would lead to similar patterns of outcomes (a correlation between lax gun regulations and high violence).

A new article by Arindrajit Dube, Oeindrila Dube and Omar Garcia-Ponce in the American Political Science Review tries to figure out what causes what, by looking at how US gun availability spills over into Mexico. Specifically, they look at how the lapsing of the Federal Assault Weapons Ban affected gun violence in parts of Mexico that bordered the US. Because the ban lapsed after 10 years (it was passed with a sunset rule), and was passed in the US rather than Mexico, it is hard to claim that it was relaxed in response to an increased risk of gun violence in Mexico. And because some states bordering Mexico (like California) continued to restrict assault weapons, while others (like Texas) did not, it is possible to reach some conclusions about how different levels of restrictions affected gun violence, by looking at e.g. differences between Mexican municipalities close to the Californian border, and municipalities close to the Texan border.

The authors find that “increased access to guns leads to more violence.” However, where increased gun access really has consequences is in “areas facing higher levels of instability — i.e., guns act as tinder in regions characterized by lawlessness and in-fighting among criminal organizations.” Dube, Dube and Garcia-Ponce argue that increased political competition in some parts of Mexico led to increased instability. Crime bosses found it harder to get long term protection from politicians who might get turfed out at the next election, and turned to gang warfare to protect and extend their territories. The results are striking.

Overall, our preferred estimates indicate that the annual additional deaths due to [the expiration of the ban] represent around 21% of all homicides and 30% of all gun-related homicides in the post-intervention sample, which are sizable magnitudes. … For total homicides there is a clear, sharp rise between 2004 and 2005 and the effect mostly persists through 2006. The results for gun-related homicides is noisier, but the same pattern is reproduced here as well.

More generally:

The potential cross-border benefits arising from U.S. gun control policy also apply more generally, beyond Mexico. The combination of its size and the fact that it has one of [the] most permissive regulatory regimes in the world implies that U.S. gun laws can have large regional or even global consequences. For example, most crime guns seized in Jamaica over this past decade have also been traced back to the U.S., specifically to the state of Florida …. Up to 80% of the guns in Central America may also originate from the U.S. …: some were transferred during past civil wars, while others have arrived more recently in conjunction with the drug trade (World Bank 2010). The diffusion of these arms appear to be exacerbating gang related violence in the previously conflict-affected nations of Guatemala, El Salvador, and Nicaragua …, while spreading to the previously peaceful nations of Costa Rica and Panama