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.

The unrestrained assault by Yugoslav military, police and paramilitary forces, under the direction of President Milosevic, on Kosovar civilians has created a massive humanitarian catastrophe which also threatens to destabilise the surrounding region.

The battalion secured AH-64 Apache attack helicopter refueling sites, and a small team forward deployed to the Albania – Kosovo border to identify targets for NATO air strikes.

"Dual-use" targets, used by civilians and military, were attacked, including bridges across the Danube, factories, power stations, telecommunications facilities, the headquarters of Yugoslav Leftists, a political party led by Milošević's wife, and the Avala TV Tower.

[76] Showing video footage, General Wesley Clark later apologized and stated that the train had been traveling too fast and the bomb was too close to the target for it to divert in time.

An October 1999 investigation by The Observer and Politiken argued that the bombing had actually been deliberate as the Embassy was being used to transmit Yugoslav army communications, something that NATO, the UK and the USA emphatically denied.

[109][110] The Yugoslav side and its Western supporters claimed the refugee outflows were caused by a mass panic in the Kosovo Albanian population, and that the exodus was generated principally by fear of NATO bombs.

United States Air Force F-15s and F-16s flying from Italian airforce bases attacked the defending Yugoslav fighters, mainly MiG-29s, which were in poor condition due to a lack of spare parts and maintenance.

The standard tactic for F-16CJs was for two pairs to come at a suspected air defence site from opposite directions, ensuring total coverage of the target area, and relaying information to incoming strike craft so they could adjust their flight path accordingly.

The EA-6Bs were noticeably slower than other aircraft, limiting their effectiveness in providing support, and land-based Prowlers flying out of Aviano Air Base were forced to carry extra fuel tanks instead of HARMs due to the distances involved.

The results were less than satisfactory: response times to engaging a SAM threat actually increased from the Gulf War, and electronic warfare wings could no longer reprogram their own jamming pods but had to send them elsewhere for the task.

In particular this applied to early-warning radars located in Montenegro, which remained operational during the campaign and gave Yugoslav forces advanced warning of incoming NATO air raids.

A common tactic was to target the last aircraft in a departing formation, on the assumption that it received less protection, was flown by a less-experienced pilot, and/or was low on fuel needed to make evasive manoeuvres.

[140] While not directly related to the hostilities, on 12 March 1999 the Czech Republic, Hungary, and Poland joined NATO by depositing instruments of accession in accordance with Article 10 of the North Atlantic Treaty at a ceremony in Independence, Missouri.

The unit was deployed in March 1999 to Albania in support of the bombing campaign where the battalion secured the Tirana airfield, Apache helicopter refueling sites, established a forward-operating base to prepare for Multiple Launch Rocket System (MLRS) strikes and offensive ground operations, and deployed a small team with an AN/TPQ-36 Firefinder radar system to the Albania/Kosovo border where it acquired targets for NATO air strikes.

Immediately after the bombing campaign, the battalion was refitted back at Tirana airfield and issued orders to move into Kosovo as the initial entry force in support of Operation Joint Guardian.

[165] In 2013, Serbia's then-defence minister Aleksandar Vučić announced that the combined Yugoslav military and law enforcement casualties during the air campaign amounted to 956 killed and 52 missing.

This stage of the campaign led to controversial incidents, most notably the bombing of the People's Republic of China embassy in Belgrade where three Chinese reporters were killed and twenty injured, which NATO claimed was a mistake.

[187][188] NATO bombing also resulted in the damaging of medieval monuments, such as Gračanica Monastery, the Patriarchate of Peć and the Visoki Dečani, which are on the UNESCO's World Heritage list today.

[190] The use of Depleted Uranium ammunition was noted by the UNEP, which cautioned about the risks for future groundwater contamination and recounted the "decontamination measures conducted by Yugoslavian, Serbian and Montenegrin authorities.

[192][193] In early June, a Finnish-Russian mediation team headed by Martti Ahtisaari and Viktor Chernomyrdin traveled to Belgrade to meet with Milošević for talks on an agreement that would suspend air strikes.

[220] Outpost Gunner was established on a high point in the Preševo Valley by Echo Battery 1/161 Field Artillery in an attempt to monitor and assist with peacekeeping efforts in the Russian sector.

US President Bill Clinton's Secretary of Defense, William Cohen, said, "The appalling accounts of mass killing in Kosovo and the pictures of refugees fleeing Serb oppression for their lives makes it clear that this is a fight for justice over genocide.

CNN reported, "Accusing Serbia of 'ethnic cleansing' in Kosovo similar to the genocide of Jews in World War II, an impassioned Clinton sought Tuesday to rally public support for his decision to send US forces into combat against Yugoslavia, a prospect that seemed increasingly likely with the breakdown of a diplomatic peace effort.

[234] The United States House of Representatives passed a non-binding resolution on 11 March 1999 by a vote of 219–191 conditionally approving of President Clinton's plan to commit 4,000 troops to the NATO peacekeeping mission.

[240] Other journalists have asserted that NATO's campaign triggered or accelerated the ethnic cleansing in Kosovo, which was the opposite of the alliance's stated aim, as prior to it Yugoslav forces limited their activities.

[241][242][243] In an interview with Radio-Television Serbia journalist Danilo Mandić on 25 April 2006, Noam Chomsky referred to the foreword to John Norris' 2005 book Collision Course: NATO, Russia, and Kosovo, in which Strobe Talbott, the Deputy Secretary of State under President Clinton and the leading US negotiator during the war, had written that "It was Yugoslavia's resistance to the broader trends of political and economic reform—not the plight of Kosovar Albanians—that best explains NATO's war.

The issue was brought before the UNSC by Russia, in a draft resolution which, inter-alia, would affirm "that such unilateral use of force constitutes a flagrant violation of the United Nations Charter".

"[250][251] Israeli Minister of Foreign Affairs Ariel Sharon criticised the NATO bombing of Yugoslavia as an act of "brutal interventionism" and said Israel was against "aggressive actions" and "hurting innocent people" and hoped "the sides will return to the negotiating table as soon as possible".

[254] Despite objections that Yugoslavia had legal jurisdiction to sue Belgium, the Netherlands, Canada and Portugal,[254] the ICJ majority vote also determined that the NATO bombing was an instance of "humanitarian intervention" and thus did not violate Article 9 of the Genocide Convention.