Countries across the globe increasingly militarize law enforcement in response to security threats. However, the extant scholarship suggests that militarizing law enforcement has negative domestic implications: more violence and abuse of human rights, and less taxation, public support for police reform, and trust in law enforcement. While research on state-society relations suggests that a strong civil society can help insulate communities from crime and organized violence, other studies argue that civil society is vulnerable to the negative, potentially violent effects of having high levels of social capital and capacity for collective action, such as turns to vigilantism. How does increased militarization affect the strength of civil society and its ability to protect citizens in times of threat? This paper examines how militarization affects civil society’s capacity to provide services and respond to security threats, along three dimensions: service provision, organizational capacity, and local social capital. I argue that militarization erodes all three dimensions over time, resulting in an overall decreased local collective action capacity and ability of civil society to insulate the public from security threats. I find preliminary empirical support for these notions using data on militarized crime-fighting policies, civil society organizations’ service delivery records, and public attitudes from Mexico and Colombia from 2006 to 2023. This project contributes to debates about militarizing public security and has implications for preserving civil society in times of threat.