This study conducts the reader on a historical walk through the military, social and economic events that would lead to the Second Great War. The author reviews these episodes to demonstrate the importance, little recognized, of the participation of the Brazilian Expeditionary Force (FEB) in the conflict. The work includes a reflection on the effects of the Second World War on international relations and on the creation of international public law, as well as on the advance of public ethics. It also examines the conflict’s effects in Brazil, Italy, Germany and Japan, and the good relations of the country with other nations post-war.