<p>This study investigates the long-term relationship between ethnic and religious diversity, democratic performance, and lethal violence in the United States from 1945 to 2023. This study is particularly important in the context of the United States, where growing diversity shapes the nation’s social and political dynamics. Lethal violence is defined as the combined total of suicides and homicides. Using the bound testing approach and the Autoregressive Distributed Lag (ARDL) model, the analysis reveals a significant positive association between increased ethnic and religious diversity and higher levels of lethal violence, with this relationship holding for both suicides and homicides. In contrast, stronger democratic performance is found to have a significant negative relationship with lethal violence. These findings suggest that while diversity may pose challenges to social cohesion, the strength of democratic institutions can play a crucial role in mitigating its potential for violence. The study highlights the critical importance of democratic governance in promoting social stability within increasingly diverse societies.</p>