This study examines the correlation between government expenditure on internal security and battle-related deaths in Nigeria, particularly in light of Sustainable Development Goal (SDG) 16, which promotes peace, justice, and strong institutions. Utilizing data from 2000 to 2022, this research applies a correlational model to analyze the relationship between internal security spending and conflict-related fatalities. Findings reveal a significant positive correlation (0.8538) between security expenditure and battle-related deaths, suggesting that while heightened spending may target conflict reduction, it has yet to achieve a decline in fatalities. The study explores potential explanations for this outcome, including resource allocation toward addressing surface-level symptoms rather than underlying socioeconomic grievances that fuel violence. Additionally, mismanagement and corruption within security agencies, compounded by external pressures like regional instability, are identified as factors that might hinder the effectiveness of internal security expenditure. These findings underscore the necessity of balancing militarized responses with socioeconomic investments to achieve sustainable peace. The study recommends implementing community-centered security initiatives, enhanced training for security forces, and better coordination among security agencies to improve conflict resolution and reduce violence.