The formal indivisibility of security, which theorists in the field of international relations speak of, is an indisputable thing. Although the development of military technology, the format of globalization, a critical attitude towards classical geopolitics have led to an underestimation of the spatial factor, regionalisation has once again proved that it is an integral part of globalisation and its alter ego. At the beginning of the third decade of the 21st century, political developments in Europe are closely connected with military security. Although this interdependence is not new, the regional security system has been relatively stable for quite some time. The steadily, albeit gradually aggravating situation around the Kaliningrad region and the Republic of Belarus has caused a response - coordinated cooperation in the framework of the Union State. The consequence of which was the formation of a sub-regional security complex (SRSC), which includes the Republic of Belarus and Russia's Kaliningrad region. And a theoretical justification for the formation of this complex is the focus of this article. The authors determine the floating boundaries of the SRSC, where spatial effects of military-political ties take on a special character. This study aims to apply and adapt the concept of regional security complexes to the military-political space of the eastern part of the Baltic Sea. The practical implications of this research include substantiating the interconnectedness and interdependence of security doctrines and practices in a troubled region of Europe.
