Abstract
The development of the fundamental principles of international relations, which flow from the UN Charter, other treaties and international custom, has changed the understanding of the legal nature of states’ international obligations. In this context, the 1994 Budapest Memorandum on Security Assurances is also a source of international obligations for the states involved. Given the importance of international community interests that are protected by jus contra bellum , the prohibition of the use of force can be regarded as a norm of jus cogens . The inherent right of states to self-defence is not covered by the scope of the prohibition of the use of force and cannot be understood as a derogation from the jus cogens norm. Finally, unilateral declarations of states may also have the effect of creating certain legal obligations in the context of jus contra bellum .