Moise Tshombe
In September 1961, during the Congo Crisis, Hammarskjöld learned about fighting between "non-combatant" UN forces and Katangese troops of Moise Tshombe. On 18 September, Hammarskjöld was en route to negotiate a cease-fire when the aircraft he was flying in crashed near Ndola, Northern Rhodesia (now Zambia). Hammarskjöld and fifteen others perished in the crash. The crash set off a succession crisis at the United Nations, as Hammarskjöld's death required the Security Council to vote on a successor.