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Somali people in the Horn of Africa are divided among different countries (Somalia, Djibouti, Ethiopia, and northeastern Kenya) that were artificially and some might say arbitrarily partitioned by the former imperial powers. Pan-Somalism is an ideology that advocates the unification of all ethnic Somalis once part of Somali empires such as the Ajuran Empire, the Adal Sultanate, the Gobroon Dynasty and the Dervish State under one flag and one nation. The Siad Barre regime actively promoted Pan-Somalism, which eventually led to the Ogaden War between Somalia on one side, and Ethiopia, Cuba and the Soviet Union on the other.

What is the name of the idea that believes all ethnic Somalis should live in the same country?
Pan-Somalism