Army (SPLA) emerged to challenge the hegemony of Khartoum. Emperor Haile Selassie had been instrumental in mediating an end to the Sudanese civil war in 1972. However, Ethiopia regularly expressed disappointment that the Sudanese government had not prevented Eritrean guerrillas from operating out of its territory. Sudan attempted to negotiate an end to the Eritrean conflict in 1975 but was unsuccessful. When Ethiopia turned to the Soviet Union and away from the United States, Sudan's government became concerned. Sudanese president Jaafar an Nimeiri had accused the Soviet Union of having inspired coup attempts against his regime in 1971 and 1976. Sudan recalled its ambassador to Ethiopia in January 1977, and for several years serious border tensions existed between the two countries.

Ethiopia's turn toward the Soviet Union caused Sudanto seek the support of new allies in preparing for the possibility of external invasions sponsored by Khartoum's regional enemies. Nimeiri decided to openly support certain Eritrean liberation movements. In addition, he supported Somalia during the Ogaden War. Nimeiri claimed that he wanted to build a "high wall against communism" in the Horn of Africa and agreed to participate with the United States, Kenya, Egypt, Somalia, and Oman in the development of the RDF. By 1980 the tensions between Sudan and Ethiopia had abated, however, with the signing of a peace treaty calling for the mutual respect of the territorial integrity and sovereignty of the two countries.

The 1981 tripartite agreement among Ethiopia, Libya, and South Yemen undermined relations between Addis Ababa and Khartoum. For some time, the Libyan