Kosovo War: Operation Joint Guardian begins when a NATO-led United Nations peacekeeping force, Kosovo Force (KFor), enters the province of Kosovo in the Federal Republic of Yugoslavia.

The Kosovo War was an armed conflict in Kosovo that lasted from 28 February 1998 until 11 June 1999. It was fought between the forces of the Federal Republic of Yugoslavia (FRY), which controlled Kosovo before the war, and the Kosovo Albanian separatist militia 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 Kosovo Force (KFOR) is a NATO-led international peacekeeping force and military of Kosovo. KFOR is the third security responder, after the Kosovo Police and the EU Rule of Law (EULEX) mission, respectively, with whom NATO peacekeeping forces work in close coordination. Its operations are gradually reducing until the Kosovo Security Force, established in 2009, becomes self-sufficient.

The North Atlantic Treaty Organization, also called the North Atlantic Alliance, is an intergovernmental military alliance between 32 member states—30 in Europe and 2 in North America. Founded in the aftermath of World War II, NATO was established with the signing of the North Atlantic Treaty in 1949. The organization serves as a system of collective security, whereby its independent member states agree to mutual defence in response to an attack by any external party. This is enshrined in Article 5 of the treaty, which states that an armed attack against one member shall be considered an attack against them all.

Kosovo, officially the Republic of Kosovo, is a landlocked country in Southeast Europe with partial diplomatic recognition. It is bordered by Albania to the southwest, Montenegro to the west, Serbia to the north and east, and North Macedonia to the southeast. It covers an area of 10,887 km² (4,203 sq mi) and has a population of nearly 1.6 million, with ethnic Albanians making up roughly 92% of the population. Kosovo has a varied terrain, with high plains along with rolling hills and mountains, some of which have an altitude over 2,500 m (8,200 ft). Its climate is mainly continental with some Mediterranean and alpine influences. Kosovo's capital and most populous city is Pristina; other major cities and urban areas include Prizren, Ferizaj, Gjilan and Peja.