On 14 July 1960 , the UN established United Nations Operation in the Congo ( UNOC ) , the largest military force of its early decades , to bring order to the breakaway State of Katanga , restoring it to the control of the Democratic Republic of the Congo by 11 May 1964 . While travelling to meet rebel leader Moise Tshombe during the conflict , Dag Hammarskjöld , often named as one of the UN 's most effective Secretaries-General , died in a plane crash ; months later he was posthumously awarded the Nobel Peace Prize . In 1964 , Hammarskjöld 's successor , U Thant , deployed the UN Peacekeeping Force in Cyprus , which would become one of the UN 's longest-running peacekeeping missions
died in a plane crash
1961 Ndola United Nations DC-6 crash
United Nations