Organized violence and crime have become major threats to security, national unity, and integration in Nigeria, with far-reaching socio-economic, political, and psychological consequences. This study examined the impact of organized violence and crime on security, national unity, and integration in Nigeria, using evidence from seven major cities: Aba, Benin, Kano, Kaduna, Abuja, Ibadan, and Lagos. The study adopted a qualitative research design and generated data through 28 Key Informant Interviews (KIIs) and 14 Focus Group Discussions (FGDs) involving security personnel, community leaders, traders, victims of crime, youths, and other relevant stakeholders. Data were analyzed using thematic content analysis. Findings revealed that organized violence and crime have significantly undermined public safety through increased incidences of kidnapping, armed robbery, cultism, and other violent crimes, creating widespread fear and insecurity among citizens. The study further found that organized violence has disrupted agricultural production, contributed to food insecurity, weakened local economies, reduced domestic and foreign investment, and increased poverty levels. In addition, the findings showed that organized violence has deepened ethnic and religious polarization, eroded public trust in government institutions, encouraged vigilantism, and weakened national cohesion and integration. The study concludes that organized violence poses a serious threat not only to human security but also to nation-building and sustainable development in Nigeria. It recommends strengthening security institutions, improving governance and justice delivery, promoting economic empowerment, enhancing arms control measures, and implementing peacebuilding initiatives aimed at fostering national unity and social cohesion.