Abstract: At the turn of the 20th - 21st centuries Yugoslavia disintegrated, ending with Montenegro’s proclamation of independence. The author of this article demonstrates the role of outside international actors in the detachment of Montenegro. The United States supported the establishment of the Belgrade agreement, developed with the active participation of the European Union, and the adoption on its basis of the Constitutional Charter of Serbia and Montenegro, which provided for the possibility of holding a referendum after three years on the withdrawal of one of the republics from the state community. Having taken part in the preparation of the referendum and renouncing the right cemented in the Belgrade Agreement to regulate disputes between Belgrade and Podgorica in the economic sphere, the European Union effectively contributed to the secession of Montenegro. The author convincingly argues with critics who do not see the guilt of the European Union in taking responsibility for the region but not wishing to take real steps to preserve the unified union state of Serbia and Montenegro. The author examines the issues from the positions of universal, general and global history, applying the multi-disciplinary and interdisciplinary approaches, and using the historical and logical methods. The author comes to the conclusion that in the 2000s the United States and the European Union played an important role in resolving the internal political issues of the states in the post-Yugoslavia space (including monitoring the change in the Yugoslavian constitution and the transformation of one state (the Federal Republic of Yugoslavia) into another (Serbia and Montenegro), and the regulation of the rules for conducting a referendum on the independence of Montenegro), which is unacceptable from the standpoint of respecting the principles sovereignty, freedom and democracy. The results of this research are not only new but can also be of practical use both in scientific research and in the activity of political forces.