15 July 1960
United Nations (UN) troops arrived to help deal with the political crisis following MoÁ¯se-Kapenda Tshombé's declaration of independence for Katanga province on 11 July. The intervention by UN troops followed Patrice Lumumba’s request for assistance from African countries and the United Nations. The secession of Katanga fuelled the province of South Kasai to declare independence on 8 August 1960, calling itself the Federal State of South Kasai, with Joseph Ngalula as head of parliament. The events leading to the secession of the two Congo provinces happened shortly after the country gained independence from Belgium on 30 June 1960.
References

Boddy-Evan, A. ‘This Day in African History: 15 July’, from About African History, [online], available at https://africanhistory.about.com (Accessed: 18 June 2013)|

South African History Online, ‘UN troops arrive to help deal with the political crisis following Moïse-Kapenda Tshombe's declaration of independence for Kata’, [online], available at www.sahistory.org.za (Accessed: 19 June 2013)|

Global Nonviolent Action Database, ‘Congolese win independence from the Belgian Empire, 1959-60’, [online], available at https://nvdatabase.swarthmore.edu (Accessed: 12 July 2013)|

Mwakikagile, G. (2009), ‘Africa 1960-1970: Chronicle and Analysis’, (New Africa Press Dar es Salaam, Tanzania) p.24