The involvement of the Soviets split the Congolese government and led to an impasse between Lumumba and President Joseph Kasa-Vubu . Mobutu , in command of the army , broke this deadlock with a coup d'état , expelled the Soviet advisors and established a new government effectively under his own control . Lumumba was taken captive and subsequently executed in 1961 . A rival government of the " Free Republic of the Congo " was founded in the eastern city of Stanleyville by Lumumba supporters led by Antoine Gizenga . It gained Soviet support but was crushed in early 1962 . Meanwhile , the UN took a more aggressive stance towards the secessionists after Hammarskjöld was killed in a plane crash in late 1961 . Supported by UN troops , Léopoldville defeated secessionist movements in Katanga and South Kasai by the start of 1963
a plane crash
1961 Ndola United Nations DC-6 crash
Congo Crisis