Following horrible experiences of the World War II, States have agreed to outlaw the use of force and the threat of force directed against territorial integrity and political independence of any state, as well as force which would in any way be inconsistent with the principles and purposes of the United Nations. This prohibition, contained in Article 2(4) of the United Nations Charter, did not, however, prevent the occurrence of numerous armed conflicts across the world. Such disobeyance of this Charter provision made many believe that due to its frequent and continuing violations the norm has simply become ineffective and does not legally bind states any longer. In order to examine if such contentions are true, it is necessary to establish whether there has been created a practice among states which is contrary to the imperative contained in Article 2(4) and whether such a practice is accompanied by the belief of states in its legally binding character. In determining whether such a belief exists, the reaction of the international community in cases of the use of force needs to be examined. An analysis of these two elements – practice and the belief in its obligatory nature – shall reveal whether instances of the use of force by some states should be considered a violation of an existing norm forbidding the use of force, or shall be a proof of inefficiency of the norm of Article 2(4) and the emergence of a new, different norm.