The Kosovo Force (KFOR) is a NATO-led international peacekeeping force in Kosovo. Its operations are gradually reducing until Kosovo's Security Force, established in 2009, becomes self sufficient.KFOR entered Kosovo on 11 June 1999, two days after the adoption of UN Security Council Resolution 1244. At the time, Kosovo was facing a grave humanitarian crisis, with military forces from Yugoslavia in action against the Kosovo Liberation Army (KLA) in daily engagements. Nearly one million people had fled Kosovo as refugees by that time, and many did not permanently return.KFOR is gradually transferring responsibilities to the Kosovo Police and other local authorities. Currently, 28 states contribute to the KFOR, with a combined strength of approximately 4,000 military and civilian personnel.The mission was initially called Operation Joint Guardian. In 2004 the codename for the mission was changed to Operation Joint Enterprise.

The Kosovo War was an armed conflict in Kosovo that started 28 February 1998 and lasted until 11 June 1999. It was fought by the forces of the Federal Republic of Yugoslavia (i.e. Serbia and Montenegro), which controlled Kosovo before the war, and the Kosovo Albanian rebel group known as the Kosovo Liberation Army (KLA). The conflict ended when the North Atlantic Treaty Organization (NATO) intervened by beginning air strikes in March 1999 which resulted in Yugoslav forces withdrawing from Kosovo.

The KLA formed in the early 1990s to fight against Serbian persecution of Kosovo Albanians. The KLA initiated its first campaign in 1995 when it launched attacks against Serbian law enforcement in Kosovo. In June 1996, the group claimed responsibility for acts of sabotage targeting Kosovo police stations, during the Kosovo Insurgency. In 1997, the organisation acquired a large amount of arms through weapons smuggling from Albania, following a rebellion in which weapons were looted from the country's police and army posts. In early 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; this campaign killed 1,500 to 2,000 civilians and KLA combatants.After attempts at a diplomatic solution failed, NATO intervened, justifying the campaign as a "humanitarian war". This precipitated a mass expulsion of Kosovar Albanians as the Yugoslav forces continued to fight during the aerial bombing of Yugoslavia (March–June 1999). By 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 systematic campaign of terror, including murders, rapes, arsons and severe maltreatments", but that Yugoslav troops had tried to remove rather than eradicate the Albanian population.The war ended with the Kumanovo Treaty, with Yugoslav and Serb 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. After the war, a list was compiled which documented that over 13,500 people were killed or went missing during the two year conflict. The Yugoslav and Serb forces caused the displacement of between 1.2 million to 1.45 million Kosovo Albanians. After the war, around 200,000 Serbs, Romani, and other non-Albanians fled Kosovo and many of the remaining civilians were victims of abuse.The NATO bombing campaign has remained controversial. It did not gain the approval of the UN Security Council and it caused at least 488 Yugoslav civilian deaths, including substantial numbers of Kosovar refugees.