Article 2(4) of the Charter is not a blanket prohibition on the use of force; rather it limits force to be used for purposes consistent with the UN Charter but does ban force with the purpose of undermining the territorial integrity and political independence of any state.
The purpose of the current use of force is not to undermine Yugoslavia, but rather to ensure that its government adheres to international law and halts the genocide against the Kosovars. Customary international law in the area of the use of force was confirmed by the International Court of Justice as recently as 1986 (see the Nicaragua Case, merits stage, paragraph 176) and this does include the category of humanitarian intervention. International crimes such as genocide are not a matter of internal affairs and require international enforcement.
Had force been used to uphold international law in Bosnia at earlier stage, the events in Kosovo might never have taken place.
Senior Lecturer in Law
University of East London