The bloodshed, ethnic cleansing of thousands of Albanians driving them into neighbouring countries, and the potential of it to destabilize the region provoked condemnation and ultimately intervention by international organisations and agencies, such as the UN, NATO, and various INGOs.NATO countries attempted to gain authorisation from the UN Security Council for military action, but were opposed by China and Russia that indicated they would veto such a proposal. As a result, NATO launched its campaign without the UN's approval, stating that it was a humanitarian intervention. The Yugoslavs' narrative was that NATO's campaign was an illegal war of aggression against a sovereign state in violation of international law as it did not have the UN Security Council's explicit endorsement.
The bombing killed about 1,000 members of the Yugoslav security forces in addition to between 489 and 528 civilians. It destroyed bridges, industrial plants, public buildings, private businesses, as well as barracks and military installations. In the days after the Yugoslav army withdrew, over 164,000 Serbs and 24,000 Roma left Kosovo and many of the remaining non-Albanian civilians (as well as Albanians perceived as collaborators) were victims of abuse which included beatings, abductions, and murders. After Kosovo and other Yugoslav Wars, Serbia became home to the highest number of refugees and IDPs (including Kosovo Serbs) in Europe.
The NATO bombing marked the second major combat operation in its history, following its 1995 bombing campaign in Bosnia and Herzegovina. It was the first time that NATO had used military force without the expressed endorsement of the UN Security Council.
Post-strike bomb damage assessment photograph of the Kragujevac Armor and Motor Vehicle Plant Crvena Zastava, Serbia
Smoke rising in Novi Sad, Serbia after NATO bombardment in 1999
After September 1990 when the 1974 Yugoslav Constitution had been unilaterally repealed by the Socialist Republic of Serbia, Kosovo's autonomy suffered and so the region was faced with state organized oppression: from the early 1990s, Albanian language radio and television were restricted and newspapers shut down. Kosovar Albanians were fired in large numbers from public enterprises and institutions, including banks, hospitals, the post office and schools. In June 1991 the University of Priština assembly and several faculty councils were dissolved and replaced by Serbs. Kosovar Albanian teachers were prevented from entering school premises for the new school year beginning in September 1991, forcing students to study at home.
Later, Kosovar Albanians started an insurgency against Belgrade when the Kosovo Liberation Army was founded in 1996. Armed clashes between the two sides broke out in early 1998. A NATO-facilitated ceasefire was signed on 15 October, but both sides broke it two months later and fighting resumed. When the killing of 45 Kosovar Albanians in the Račak massacre was reported in January 1999, NATO decided that the conflict could only be settled by introducing a military peacekeeping force to forcibly restrain the two sides. After the Rambouillet Accords broke down on 23 March with Yugoslav rejection of an external peacekeeping force, NATO prepared to install the peacekeepers by force.