2 August 1977
Ethiopia requested the Organisation of African Unity (OAU), predecessor of the African Union to stop Somali intervention in the Ogaden Province, Ethiopia. Ethiopia’s plea to the OAU followed the attempt by Somali forces to occupy Ogaden on 23 July 1977. The Somali Army crossed the international border of Ethiopia into Ogaden Province without any resistance. The tension between the two east African countries started long before the Ogaden War. In 1976, Ethiopia distributed a 39 page memorandum titled “War Clouds in the Horn of Africa” to Heads of States attending an OAU meeting in Addis Ababa.  Its primary purpose was to warn African leaders of the growing tension between the two countries.
References

Global Security, (1986), ‘Why Ogaden War’, [online], available at www.globalsecurity.org (Accessed: 05 July 2012)|Boddy-Evans A. ‘This day in African history’, from About African History.com, 02 August, [online], available at www.africanhistory.about.com (Accessed: 05 July 2012)