The need for “decolonisation” of the Second world and semi-periphery countries (in the terminology of world-systems analysis) is increasingly raised in practical policy as well as in academic publications. However, the very question of decolonisation as applied to countries that were the targets of European colonial expansion is fraught with both negative consequences in political practice and theoretical confusion. On the one hand, the discourse of “decolonisation” encourages separatist tendencies and leads to new conflicts. On the other hand, the notion of “colonialism” is becoming less rigorous: in this perspective, any territorial expansion by any state at any time in history can be described as colonialism. The notion of “colonialism” loses its specific historical meaning and hence turns from a scientific term into a propaganda cliché. Thus, the possibility to correctly comprehend the phenomenon of European colonialism as a concrete historical reality that determined the fate of the peoples of both Europe itself and other parts of the world in Modern times, the only “colonialism” that the peoples of the world have really faced for the last 500 years, disappears. Theoretical and practical, scientific and political aspects of the problem are closely linked. Within an expansive interpretation of “colonialism”, former colonial powers, moreover, states still possessing unequal dependencies, such as the USA, are able to accuse their geopolitical opponents of “colonialism” as they are multi-ethnic powers, formed as a result of long historical processes, where various practices of ethnic interaction have taken place. The very possibility of interpreting the practices of non-European powers (Russia, China, Iran, Ethiopia) as colonial is linked to the popular paradigm of “internal colonialism.” It has emerged as part of the post-colonial theory of international relations in European and American academic centres and by its very nature is an example of a deliberately biased approach that focuses on the most marginalised groups of “subalterns” but ignores major civilisational entities. The author points out the biases and shortcomings of this approach with concrete examples, reveals its philosophical premises and suggests using the findings of fundamental geopolitics, world-systems theory, philosophy of space and philosophy of culture to clarify the concept of “colonialism.”