the country, opening the way for Congolese to replace the European military and administrative elite. Shortly after this, Moise Tshombe led a successful secessionist effort to take the wealthy Katanga province out of the new nation. At the end of 1960 President Kasa Vubu dismissed the new prime minister, Patrice Lumumba, and a week later Colonel Joseph Mobutu seized power, holding it until February 1961, by which time Lumumba had been killed. Meanwhile, Belgian troops intervened to protect Belgian nationals as civil war spread in the former Belgian colony. The assassination of Lumumba precipitated a Security Council resolution on 21 February 1961 that conferred on ONUC the ability to use force to stop the descent into civil war. Prior to this point ONUC had only been allowed to use force in self-defense. During operations in the Congo, Secretary-General Dag Hammarskjld was killed in a plane crash and was awarded the Nobel Peace Prize posthumously. Even with upwards of 20,000 UN-sponsored troops in the Congo, however, a cease-fire was not agreed to and Katanga was not brought back into the Congo until 1963. All ONUC troops were withdrawn by the end of June 1964, in part because the UN itself was on the brink of bankruptcy (a result of the French and Soviet government's refusal to contribute to the costs of ONUC). It was not until the UN operation in Somalia in 1992, almost thirty years later, that the UN again intervened militarily on the scale of its operation in the