The Ogaden War was a conventional conflict between Somalia and Ethiopia in 1977 and 1978 over the Ogaden region of Ethiopia. In a notable illustration of the nature of Cold War alliances, the Soviet Union switched from supplying aid to Somalia to supporting Ethiopia, which had previously been backed by the United States, prompting the U.S. to start supporting Somalia. The war ended when Somali forces retreated back across the border and a truce was declared.

During the Scramble for Africa, the lands inhabited by the Somali people were divided between the relevant powers. To Italy went Southern Somalia, to Britain Northern Somalia along the Gulf of Aden, to France the hinterlands of Tajoura, while Ethiopia, which had gained the respect of the European powers with its decisive victory at the Battle of Adwa, received the Ogaden region by treaty. In 1960 Britain gave independence to its colony which joined with southern Somalia to create the new state of Somalia. By the beginning of the war, the Somali National Army (SNA) was only 35,000-men strong and was vastly outnumbered by the Ethiopian forces. However, throughout the 1970s, Somalia was the recipient of large amounts of Soviet military aid. The SNA had three times the tank force of Ethiopia, and had a larger air force.

Ogaden (pronounced and often spelled Ogadēn; Somali: Ogaadeen, Amharic: ኦጋዴን^?) is the name of a territory comprising the southeastern portion of the Somali Regional State in Ethiopia. The inhabitants are predominantly ethnic Somali and Muslim. The title "Somali Galbeed", which means "Western Somalia," is often preferred by Somali irredentists.

The region, which is around 200,000 square kilometres, borders Djibouti, Kenya, and Somalia. Important towns include Jijiga (Jigjiga), Awbere, Feer Feer, Degehabur, Raaso, (Dhagaxbuur in Somali), Gode (Godey), Kebri Dahar (Qabridahare), Fiq, Shilavo (Shilaabo), Kelafo, Werder (Wardheer), and Denan.

The Ogaden is a plateau, with an elevation above sea level that ranges from 1,500 metres in the northwest, falling to about 300 metres along the southern limits and the Wabi Shebelle valley. The areas with altitudes between 1,400 and 1,600 metres are characterized as semi-arid; receiving as much as 500–600 mm of rainfall annually. More typical of the Ogaden is an average annual rainfall of 350 mm and less. The landscape consists of dense shrubland, bush grassland and bare hills. In more recent years, the Ogaden has suffered from increasingly erratic rainfall patterns, which has led to an increasing frequency of major droughts: in 1984-85; 1994; and most recently in 1999-2000, during which pastoralists claim to have lost 70-90 percent of their cattle.