International relations are presently in the midst of impressive change. Whether discussing traditional geopolitics, political and economic globalisation, international institutions, the rise of religious extremism, energy security, or enviro-politics, it is sure that the 21st century offers new challenges, and thus presents international relations scholars with new problematics to consider and address. The changing characteristics of violent conflicts require new approaches to their resolution; the use of force is no longer interpreted exclusively in terms of self-defence but also due to humanitarian necessity.

This article is meant to contribute to the wide discussion on humanitarian interventions (HI) by exploring some aspects of how they may acquire international legitimacy. The main controversies surrounding this issue, stems on one hand, from the changing practice of international relations, and from the absence of uniform decision-making system for evaluating necessity, legitimacy and success by concrete interventions on the other.

Although an exact definition of HI is absent from international conventions, it may be understood as ‘coercive interference in the internal affairs of a state involving the use of force with the purposes of addressing massive human rights violations or preventing human suffering.’ According to this specificity, the post-WWII period offers various empirical cases of HI. Nonetheless, there is, in general, insufficient support of the norm through purely legal lenses; revealing obstacles and restrictions by particular actions. Thus, the normative development of HI will be explored in this research by adopting a legitimacy approach, enabling a wider perspective to understanding the changing nature of both international order and justice.

In this context, the more traditional approaches of realism and liberalism also demonstrate explanatory poverty in terms of norm- and idea-shifts that can be supplemented by the more comprehensive theory of social constructivism. Accordingly, attention will be paid to linking HI, legitimacy and international consensus building and mobilisation. First, it is crucial to demonstrate the changing atmosphere in international politics during and after the Cold War through selected cases of HI that were undertaken with a focus on the extent of international acceptance and legitimacy each case obtained.

The empirical results will be followed by evaluating the quality of the popular framework for both justifying and criticising various HI´s namely, Just War Theory (JWT). Recently, there has been important progress achieved in defining this concept and applying it to international relations. The Commission on Intervention and State Sovereignty recommended in its report entitled ‘Responsibility to Protect’ six points that could be applied for identifying legitimacy of a HI: (i) just cause, (ii) right intention, (iii) last resort, (iv) proportional means, (v) reasonable prospects, and (vi) authorisation. The main task of this research is to identify the main advantages and limitations within this legitimacy framework to be possibly reformed to establish a more in-sync, universal applicability for future largescale humanitarian issues.