This paper studies the impacts of the military securitization of cyberspace in the international politics of the 21st century. Cyberdefense is chosen as the object of study precisely because it allows inferences to be made about the political-institutional materialization of this issue, seeking support in the theory of securitization, proposed by the Copenhagen School. In this sense, this paper seeks to: (i) identify the main existential (cyber) threats to the military sector, revealing why this process is intensifying in the 21st century; (ii) project the conditions for such securitization; and (iii) explain its effects on international politics, based on the cases of the United States, Brazil and Canada. To this end, the Spectrum of Military Securitization of Cyberspace (ESMC) is designed, a framework of analysis based on the theory of securitization with a focus on cyberdefense in a given time and space. As for the literature review, Brazilian and foreign authors in Political Science and International Relations figure mostly in the body of this work. As for the methodology, it uses the qualitative-quantitative analysis style, despite the use of interviews, case studies, discourse and document analysis. Its conclusion aims to corroborate the hypothesis that, in addition to the securitization of cyberspace by the military sector, this process is reflected in current international politics. Consequently, it is possible to situate the three cases in this ESMC.