Following all the major engagements of their invasion, Italian troops from the colony of Eritrea entered Addis Ababa on 5 May 1936. Along with Dire Dawa, the city had been spared the aerial bombardment (including the use of chemical weapons such as mustard gas) practised elsewhere in Ethiopia. This also allowed its railway to Djibouti to remain intact. After the occupation, the city served as the Duke of Aosta's capital for unified Italian East Africa until 1941, when it was abandoned in favour of Amba Alagi and other redoubts during the Second World War's East African Campaign. The city was liberated by Major Orde Wingate and negus Haile Selassie for Ethiopian Gideon Force and Ethiopian resistance in time to permit Emperor Haile Selassie's return on 5 May 1941, five years to the day after he had left. Following reconstruction, Haile Selassie helped form the Organisation of African Unity in 1963 and invited the new organisation to keep its headquarters in Addis Ababa. The OAU was dissolved in 2002 and replaced by the African Union (AU), which is also headquartered in the city. The United Nations Economic Commission for Africa also has its headquarters in Addis Ababa. Addis Ababa was also the site of the Council of the Oriental Orthodox Churches in 1965.