The legitimacy of the 1999 NATO bombing of the Federal Republic of Yugoslavia has been questioned by various parties. The key basis governing the legality of any act of war is international law. In this case, any course of action is also bound by other foundations such as the NATO and UN charters, both of which were drafted in accordance with pre-existing international regulation. Various pieces of legislation have been cited to substantiate claims as to whether or not the bombing was legal.
Supporters of the NATO bombing of Yugoslavia argued that the bombing brought to an end the ethnic cleansing of Kosovo's Albanian population, and that it hastened (or caused) the downfall of Slobodan Milošević's government, which they saw as having been responsible for the international isolation of Yugoslavia, war crimes, and human rights violations.
Others view the action as of dubious legality. Some opponents of the bombing have argued that NATO targeted non-military buildings, resulting in civilian casualties.
NATO described the conditions in Kosovo as posing a risk to regional stability. As such, NATO and certain governments asserted they had a legitimate interest in developments in Kosovo, due to their impact on the stability of the whole region which, they claimed, is a legitimate concern of the Organisation.
The prohibition against the use of force in the UN Charter can be found in article 2(4) with two specific exceptions against this prohibition provided for in the Charter. The first is in Chapter VII, where the Security Council has been given power in order to fulfill its responsibility for the maintenance of international peace and security. Article 42 states that should the Security Council consider that measures provided for in Article 41 would be inadequate or have proved to be inadequate, it may take such action by air, sea, or land forces as may be necessary to maintain or restore international peace and security. Such action may include demonstrations, blockade, and other operations by air, sea, or land forces of Members of the United Nations.