Kyiv Rus was an early medieval state in Eastern Europe centered in Kyiv, which now is the capital of Ukraine. This paper examines the systematic distortion of the history of Kyiv Rus by Russia as a tool for legitimizing its current territorial claims to Ukraine. The author analyzes the methods of historical falsification used from the eighteenth century to the present day, as well as their impact on the formation of public opinion and international relations. Based on a content analysis of key Russian historiographical and educational texts, this study outlines the mechanisms of historical falsification, including selective interpretation of sources, the construction of imperial myths, and the institutional dissemination of the narrative of the “common origin” of Russians and Ukrainians. The connection between these falsifications and the current Russian aggression against Ukraine, as well as their implications for international security, is also considered.