Civil-military relations (CMR) are the relationships that exist between the civilian authority (CAU) and non-governmental civilian groups (NGCG) versus the military. While peacebuilding is a method of capacity building and reconciliation that is aimed at preventing conflict or the restart of it. The study examines the nature and character of civil-military relations and peace building in South West Nigeria, 2011-2018. The research method adopted for this study is a documentary method, using content analysis to analyze the content of the work. Observation and documentary studies were an instrument of collecting data for the research work. The theory employed for this study is agency theory. Findings revealed that: there is a constitutional provision that provides for the subordination of the military to civilian authority, hence the military willingly accept their subordinate position to the civilian authority or his representatives; Further findings show that; there were conflicts between the non-governmental civilian groups and the military, hence negative peace existed between them; the conflicts between both parties are in the area of harassment and intimidation of the masses. The study recommended that: the National Assembly should enact a law that will make only retired military officers to be appointed as minister of Defence and Police respectively. Again, Independent Monitoring Operation on Military (IMOM) should be set up by the National Assembly from among the non-governmental civilian groups to monitor the movement of soldiers and their activities, with power to sanction and punish soldiers.