The author highlights the current problems of the Ukrainian state in the context of Russia's large-scale war against Ukraine. The importance of studying the religious factor and its impact on Ukraine's national security is substantiated. It is shown how, with the “spiritual” support of its original assistant, the Russian Orthodox Church (ROC), the Moscow Patriarchate in Ukraine in the guise of the so-called Ukrainian Orthodox Church (UOC-MP) has been actively proclaiming the “gathering of Russian lands” for decades. This “hostile tandem” has been building a “Russian world” on Ukrainian territory with intolerance to everything Ukrainian, pursuing a collaborationist policy in Ukraine, lobbying for Russia's interests, and becoming an important tool for influencing the minds of a large number of people. With the restoration of the independence of the Ukrainian state, Orthodoxy was supposed to become a consolidating factor in the creation of the Ukrainian nation. Instead, for decades, the UOC-MP has been constantly deconsolidating Ukrainian society, sowing church discord, and discrediting Ukraine's political and spiritual leadership in the international arena. Such activities have resulted in not only the territorial but also the spiritual occupation of our country. It is concluded that the concept of the “Russian world”, cultivated for years in Ukraine by the Kremlin through its “Orthodox” structures of the Russian Orthodox Church and the UOC-MP, was mainly the basis for the invasion of Ukrainian territories by the occupiers, which later escalated into a large-scale national liberation war in 2022. The study used data from sociological services, official documents of church institutions, and analyzed Ukrainian legislation on related issues. Certain provisions of the study can be used to further analyze the activities and spheres of influence of the Moscow Patriarchate in order to prevent similar tragedies in the future.