The laws of public international law that determine whether launching a war is legally justified are called jus ad bellum.
NATO's argument for the bombing's legitimacy
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 UN Charter is legally binding on all United Nations member states, including all members of NATO, because they have each signed it. Article 2 of the UN Charter prohibits the use of force by UN member states to resolve disputes, but with two specific exceptions to this general prohibition: NATO did not have the backing of the United Nations Security Council to use force in Yugoslavia. Further, NATO did not claim that an armed attack occurred against another state. However, its advocates contend that NATO actions were consistent with the United Nations Charter because the UN Charter prohibits unprovoked attacks only by individual states. The principal legal issue remains, however, since NATO as such is not a member state of the UN, whether the member states of NATO, the United States and the European powers that sent armed forces to attack as part of the NATO bombing campaign, violated the UN Charter by attacking a fellow UN member state: in the absence of UN Security Council authorization, and in the absence of an attack or a threat of imminent attack on them. The United Nations considers NATO to be a "regional arrangement" under UN Article 52, which allows it to deal with matters relating to the maintenance of international peace and security as are appropriate for regional action provided that such arrangements or agencies and their activities are consistent with the Purposes and Principles of the United Nations. However, the UN policy on military intervention by regional arrangements in UN Article 53 states the Security Council can, where appropriate, "utilize such regional arrangements or agencies for enforcement action under its authority. However, no enforcement action shall be taken under regional arrangements or by regional agencies without the authorization of the Security Council."
NATO's charter
NATO had justified the actions in Kosovo under Article 4 of its charter, the North Atlantic Treaty, which allows involved parties to consult together whenever political independence or security of any of the parties is threatened. Because the NATO actions in Kosovo were taken after consultation with all members, were approved by a NATO vote, and were undertaken by several NATO members, NATO contends that its actions were in accordance with its charter. Article 4, however, is silent as to the use of force and does not discuss under what circumstances force may be authorized. Article 5 of NATO's charter calls on NATO members to respond in mutual defense when any NATO member is attacked. It is unclear whether under the NATO charter force may be used in the absence of such an attack. Article 5 has been interpreted as restricting NATO's use of force to situations where a NATO member has been attacked. It has been argued, therefore, that NATO's actions were in violation of the charter of NATO. Critics of this theory argue, however, that the purpose of Article 5 is to require all NATO members to respond when any NATO member is attacked, not to restrict the circumstances under which NATO may choose to use force.
The Vienna Convention
Serbia was threatened by NATO with armed attack if Serbia refused to sign the Rambouillet Agreement, an agreement that Serbia in the end refused to sign. It has been argued that pursuant to Article 52 of the 1980 Vienna Convention on the Law of Treaties, had Serbia signed the Rambouillet Agreement, the agreement would have been void due to the threat or use of force to compel Serbian acceptance.
International criticism NATO actions
Kofi Annan
supported intervention in principle, saying "there are times when the use of force may be legitimate in the pursuit of peace", but was critical of unilateral action by NATO. He argued "under the Charter the Security Council has primary responsibility for maintaining international peace and security - and this is explicitly acknowledged in the North Atlantic Treaty. Therefore, the Council should be involved in any decision to resort to the use of force."
Russian attempt to end the bombing
On the day the bombing started, Russia called for the UN Security Council to meet to consider "an extremely dangerous situation caused by the unilateral military action of the North Atlantic Treaty Organization against the Federal Republic of Yugoslavia". However, a draft resolution, tabled jointly by Russia, Belarus and India, to demand "an immediate cessation of the use of force against the Federal Republic of Yugoslavia" was defeated. Among the 15 UN Security Council nations, there were three votes in favour and twelve against, with no abstentions. Argentina, Bahrain, Brazil, Gabon, Gambia, Malaysia, and Slovenia, along with the US, Britain, France, Canada, and Netherlands voted against it. Rejection of Russia's condemnation amounted to political, but not legal, support of NATO's intervention. After the war ended with the Kumanovo Treaty and the bombing stopped, some argued that the creation on 10 June 1999 of the UN Interim Administration Mission in Kosovo, by Security Council Resolution 1244, constituted a legal ratification post festum.
Humanitarian reasoning
The bombing campaign is sometimes referred to as a "humanitarian war" or a case of "humanitarian intervention". Part of NATO's justification for the bombing was to end the humanitarian crisis involving the large outflow of Kosovar Albanian refugees caused by Yugoslav forces. In April 1999, the development of this humanitarian crisis as well as accusations of genocide were used by policy-makers in the United States and Europe to legally justify the campaign on the basis of "humanitarian law", allowing for intervention where large scale human rights violations are occurring. Human rights organizations and individuals were divided on the campaign, given that the invocation of human rights and humanitarian law was used to initiate war. Moreover, they expressed doubts about the campaign given that it worsened the violence against Kosovar Albanians. Critics of the campaign have employed the term "humanitarian bombing" in an ironic manner to demonstrate their derision.
, former Canadian ambassador to Yugoslavia, Bulgaria, and Albania, said in 2004 that "Canada participated in a series of NATO-sanctioned war crimes against Yugoslavia". He added, "NATO and the United States claimed that more than 100,000 ethnic Albanians had been killed as the result of Serb genocide". "The forensic experts found fewer than 2,000 graves and many of the people in those graves were Serbs," Bissett claimed. According to Bissett, "There were more civilians killed in Serbia by the NATO bombing campaign."
Noam Chomsky
was also highly critical of the NATO campaign and its aerial bombing in particular, where public utilities were bombed in addition to military targets. Chomsky argued that the main objective of the NATO intervention was to integrate FR Yugoslavia into the Western neo-liberal social and economic system, since it was the only country in the region which still defied the Western hegemony prior to 1999. He described bombing of the Radio Television of Serbia as an act of terrorism.
