18 August 1967
Umkhonto we Sizwe (MK), the military wing of the African National Congress (ANC) and the Zimbabwean People’s Revolutionary Army (ZIPRA), military wing of Zimbabwean African People’s Union (ZAPU) formally announced that they had formed a military alliance. The guerrillas clashed with Rhodesian and South African forces in Wankie and Sipolilo Campaign in Rhodesia. Their fighting ability amazed their enemies as they thought it was going to be a cat and mouse clash. The conflict lasted until late in 1968 and observers believe that it sent a strong message to the Rhodesian and South African governments that guerrilla warfare would soon engulf the region.    
References

South African History Online‘Luthuli Combat Detachment crosses the Zambezi’, [online], available at www.sahistory.org.za [Accessed: 16 August 2013]|Mwakikagile Godfrey (2009), ‘Africa 1960-1970 Chronicles and Analysis, (New Africa Press), p. 518