The article deals with the problem of moral justification of humanitarian intervention by modern just war theorists. At the beginning of the article, we discuss the evolution of the dominant paradigms of the moral justification of war and explain why the theory and practice of humanitarian intervention appears only at the present stage of the development of ethics and the law of war. It is noted that theorization of humanitarian intervention began in the last decades of the 20thcentury. This is due to a significant transformation, a retreat in the legal and ethical studies of war from the position of radical condemnation of aggressive actions and the recognition of the political subjectivity of non-state groups. Thus, there is a rethinking of the long tradition, the Westphalian system of international relations, according to which the state was recognized as the main participant of big politics, and its sovereign right to conduct domestic policy was considered indisputable. Further, we take the works of Michael Walzer as the main source of modern conceptualization of the ethics of humanitarian interventionism, since Walzer repeatedly addressed this topic and formulated a position on this issue that is representative of the entire modern Just War Theory. The arguments of Walzer and his supporters in favor of the moral justification of humanitarian intervention are considered. Among them are the following. First, the argument about the state as an organization which goal is to protect the rights of its own citizens. If this goal is not not achieved, the state shall loose its power over these people and in this territory. Second, Walzer calls for identifying governments and armed forces involved in mass murders as criminal and, therefore, deserving of punishment. Finally, there is, perhaps the most important, demonstrative argument: an appeal to the self-evident impossibility to stand aside in cases of mass violence in any state. This is followed by a critique of these arguments, as well as a demonstration of how the modern Just War Theory can respond to these criticisms.