American gun ownership and the ingroup/outgroup divide.

American protective gun ownership privatizes collective behavior, transmuting the role of the state to keep citizens safe into individual actions to protect one's family and one's immediate community. In doing so, owners may sharpen the ingroup/outgroup divide into those who need protection and those who need to be protected against. Using nationally representative individual-level data from the General Social Survey, we find that American gun owners have friendship structures that are more ingroup-focused than nonowners: more cohesive (more of owners' friends are friends with each other) and less diverse (fewer of owners' friends are of different races or religions). Using county-aggregated data from over 70 million Facebook users (over 21 billion friendship ties), we similarly find that US counties with higher rates of gun ownership have friendship structures that are more cohesive and less diverse. This is mirrored in our findings that states and counties with higher rates of firearm ownership have lower rates of social infrastructural sites that bring communities together and lower rates of civic trust. Finally, we show evidence that the presence of guns is a quasi-causal factor in declining social capital-using modern time-series analyses, we show that a state-level increase in gun sales predicts a significant decrease in the next year's rates of social capital.