Ethiopia's entry into the Somali region in modern times dated from Menelik's conquest of Harer in the late 1890s, the emperor basing his actions on old claims of Ethiopian sovereignty. In 1945 Haile Selassie, fearing the possibility of British support for a separate Somali state that would include the Ogaden, claimed Italian Somaliland as a "lost province." In Italian Somaliland, the Somali Youth League (SYL) resisted this claim and in its turn demanded unification of all Somali areas, including those in Ethiopia.

After the British evacuated the Ogaden in 1948, Ethiopian officers took over administration in the city of Jijiga, at one point suppressing a demonstration led by the SYL, which the government subsequently outlawed. At the same time, Ethiopia renounced its claim to Italian Somaliland in deference to UN calls for self-determination. The Ethiopians, however, maintained that self-determination was not incompatible with eventual union.

Immediately upon the birth of the Republic of Somalia in 1960, which followed the merger of British Somaliland and Italian Somaliland, the new country proclaimed an irredentist policy. Somalia laid claim to Somali-populated regions of French Somaliland (later called the French Territory of the Afars and Issas, and Djibouti after independence in 1977), the northeastern corner of Kenya, and the Ogaden, a vast, ill-defined region occupied by Somali nomads extending southeast from Ethiopia's southern highlands that includes a separate region east of Harer known as the Haud. The uncertainty over the precise location of the frontier between Ethiopia and the former Italian possessions in Somalia further complicated these claims. Despite UN efforts to promote an agreement, none was made in the colonial or the Italian trusteeship period.

In the northeast, an Anglo-Ethiopian treaty determined the frontier's official location. However, Somalia contended that it was unfairly placed so as to exclude the herders resident in Somalia from vital seasonal grazing lands in the Haud. The British had administered the Haud as an integral part of British Somaliland, although Ethiopian sovereignty had been recognized there. After it was disbanded in the rest of Ethiopia, the British military administration continued to supervise the area from Harer eastward and did not withdraw from the Haud until 1955. Even then, the British stressed the region's importance to Somalia by requiring the Ethiopians to guarantee the Somali free access to grazing lands.

Somalia refused to recognize any pre-1960 treaties defining the Somali-Ethiopian borders because colonial governments had concluded the agreements. Despite the need for access to pasturage for local herds, the Somali government even refused to acknowledge the British treaty guaranteeing Somali grazing rights in the Haud because it would have indirectly recognized Ethiopian sovereignty over the area.

Within six months after Somali independence, military incidents occurred between Ethiopian and Somali forces along their mutual border. Confrontations escalated again in 1964, when the Ethiopian air force27a ce raided Somali villages and encampments inside the Somali border. Hostilities were ended through mediation by the OAU and Sudan. However, Somalia continued to promote irredentism by supporting the Western Somali Liberation Front (WSLF), which was active in the Ogaden. Claims of oil discoveries prompted the resurgence of fighting in 1973.

Data as of 1991