Eritrea: Italy purchased the port of Assab from a commercial company that was administering it. Encouraged by the British, who were then attempting to contain France's colonial asspirations in the Horn, Italy proceeded to colonize the region. Italy moved to transform Eritrea, with its access to sea and agricultural potential, into a permanent colony. The king of Italy issued a decree that formally established Eritrea on 1 January 1890. Eritrea was defined as a Nation State, and a colony of Italy.
Somalia: In 1885, Italy obtained commercial advantages in the area from the sultan of Zanzibar and in 1889 concluded agreements with the sultans of Obbia and Aluula, who placed their territories under Italy's protection. Between 1897 and 1908, Italy made agreements with the Ethiopians and the British that marked out the boundaries of Italian Somaliland. The Italian Government assumed direct administration, giving the territory colonial status.
Italian occupation gradually extended inland. In 1924, the Jubaland Province of Kenya, including the town and port of Kismayo, was ceded to Italy by the United Kingdom. The subjugation and occupation of the independent sultanates of Obbia and Mijertein, begun in 1925, were completed in 1927. In the late 1920s, Italian and Somali influence expanded into the Ogaden region of eastern Ethiopia.
Following Italy's declaration of war on the United Kingdom in June 1940, Italian troops overran British Somaliland and drove out the British garrison.
Ethiopia: Menelik signed a treaty of friendship and cooperation with Italy at Wuchale in 1889. Due to a dispute over the meaning of the treaty (Italy claimed it had been given a protectorate over Ethiopia, which Menelik denied), Italy invaded Ethiopia in 1895 but was decisively defeated by Menelik's forces at Adwa on March 1, 1896.
Mussolini, who was determined to expand the Italian Empire and to avenge the defeat at Adwa. A border clash at Walwal in Southeast Ethiopia along the border with Italian Somaliland on December 5, 1934, increased tension, and on October 3, 1935, Mussolin's Legions invaded. Italy quickly defeated the Ethiopians and in May, 1936, Addis Ababa was captured and Haile Selassie fled the country. On June 1, 1936, the King of Italy, Victor Emmanuel III was also made Emperor of Ethiopia. The country was combined with Eritrea and Italian Somaliland to form Italian East Africa.
Later British Somaliland and French Somaliland would be added to Italian East Africa, After World War 2 had begun, these were quick victories.