The Kosovo War was an armed conflict in Kosovo that lasted from 28 February 1998 until 11 June 1999. It was fought by the forces of the Federal Republic of Yugoslavia, (by this time, consisting of the Republics of Montenegro and Serbia) which controlled Kosovo before the war, and the Kosovo Albanian rebel group known as the Kosovo Liberation Army (KLA) with air support from the North Atlantic Treaty Organisation (NATO), (from 24th March 1999), and ground support from the Albanian army.
The KLA, formed in 1991, initiated its first campaign in 1995 when it launched attacks targeting Serbian law enforcement in Kosovo, and in June 1996 the group claimed responsibility for acts of sabotage targeting Kosovo police stations. In 1997, the organisation acquired a large amount of arms through weapons smuggling from Albania, following a rebellion which saw large numbers of weapons looted from the country's police and army posts. In 1998, KLA attacks targeting Yugoslav authorities in Kosovo resulted in an increased presence of Serb paramilitaries and regular forces who subsequently began pursuing a campaign of retribution targeting KLA sympathisers and political opponents in a drive which left 1,500 to 2,000 KLA combatants and civilians dead. After attempts at a diplomatic solution failed, NATO intervened, justifying the campaign in Kosovo as a "humanitarian war". This precipitated a mass expulsion of Kosovars by Serbs while Yugoslav forces continued to fight during the aerial bombardment of Yugoslavia (March–June 1999). By the year 2000, investigations had recovered the remains of almost three thousand victims of all ethnicities, and in 2001 a United Nations administered Supreme Court, based in Kosovo, found that there had been a "a systematic campaign of terror, including murders, rapes, arsons and severe maltreatments", but that Serb troops had tried to remove rather than eradicate the Albanian population.
The war ended with the Kumanovo Treaty, with Yugoslav forces agreeing to withdraw from Kosovo to make way for an international presence. The Kosovo Liberation Army disbanded soon after this, with some of its members going on to fight for the UÇPMB in the Preševo Valley and others joining the National Liberation Army (NLA) and Albanian National Army (ANA) during the armed ethnic conflict in Macedonia, while others went on to form the Kosovo Police. The conflict featured in news headlines around the world for months, and gained major coverage from the international media. The NATO bombing campaign has remained controversial, as it did not gain the approval of the UN Security Council.