United Nations (UN) peacekeepers play a dual role in conflict zones by addressing security concerns and contributing to infrastructure development. While their primary mission focuses on immediate security to reduce violence, their presence indirectly impacts conflict dynamics. This study highlights two key effects of UN peacekeepers on reducing battle-related deaths. First, they deter warring parties, limiting battlefield activities. Second, their involvement in infrastructure development raises the cost of war, fostering cooperation, building local trust, and enhancing community support for UN efforts. These development initiatives foster cooperation and provide better intelligence, further reducing violence. Using novel data on infrastructure built by UN peacekeepers in three African countries from July 2010 to December 2022, this study employs mediation analysis to evaluate these effects. The findings reveal that both deterrence and infrastructure development significantly reduce violence, offering new insights into the broader impact of peacekeepers’ presence in conflict settings.