The East African campaign (also known as the Abyssinian campaign) was fought in East Africa during the Second World War by Allies of World War II, mainly from the British Empire, against Italy and its colony of Italian East Africa, between June 1940 and November 1941. The British Middle East Command with troops from the United Kingdom, South Africa, British India, Uganda Protectorate, Kenya, Somaliland, West Africa, Northern and Southern Rhodesia, Sudan and Nyasaland participated in the campaign. These were joined by the Allied Force Publique of Belgian Congo, Imperial Ethiopian Arbegnoch (resistance forces) and a small unit of Free French Forces.

Italian East Africa was defended by the Comando Forze Armate dell'Africa Orientale Italiana (Italian East African Armed Forces Command), with units from the Regio Esercito (Royal Army), Regia Aeronautica (Royal Air Force) and Regia Marina (Royal Navy). The Italian forces included about 250,000 soldiers of the Regio Corpo Truppe Coloniali (Royal Corps of Colonial Troops), led by Italian officers and NCOs. With Britain in control of the Suez Canal, the Italian forces were cut off from supplies and reinforcement once hostilities began.

On 13 June 1940, an Italian air raid took place on the RAF base at Wajir in Kenya and the air war continued until Italian forces had been pushed back from Kenya and Sudan, through Somaliland, Eritrea and Ethiopia in 1940 and early 1941. The remnants of the Italian forces in the region surrendered after the Battle of Gondar in November 1941, except for small groups that fought a guerrilla war in Ethiopia against the British until the Armistice of Cassibile in September 1943, which ended the war between Italy and the Allies. The East African campaign was the first Allied strategic victory in the war; few Italian forces escaped the region to be used in other campaigns and the Italian defeat greatly eased the flow of supplies through the Red Sea to Egypt. Most of the Commonwealth forces were transferred to North Africa to participate in the Western Desert campaign.

On 9 May 1936, the Italian dictator, Benito Mussolini, proclaimed the formation of Italian East Africa (Africa Orientale Italiana, AOI), from Ethiopia after the Second Italo-Abyssinian War and the colonies of Italian Eritrea and Italian Somaliland. On 10 June 1940, Mussolini declared war on Britain and France, which made Italian military forces in Libya a threat to Egypt and those in the AOI a danger to the British and French colonies in East Africa. Italian belligerence also closed the Mediterranean to Allied merchant ships and endangered British sea lanes along the coast of East Africa, the Gulf of Aden, the Red Sea and the Suez Canal. (The Kingdom of Egypt remained neutral during the Second World War but the terms of the Anglo-Egyptian treaty of 1936 allowed the British to occupy Egypt and Anglo-Egyptian Sudan.) Egypt, the Suez Canal, French Somaliland and British Somaliland were also vulnerable to invasion but the Italian General Staff had planned for a war after 1942; in the summer of 1940 Italy was far from ready for a long war or for the occupation of large areas of Africa.

Amedeo, Duke of Aosta, was appointed Viceroy and Governor-General of the AOI in November 1937, with a headquarters in Addis Ababa, the Ethiopian capital. On 1 June 1940, as the commander in chief of Comando Forze Armate dell'Africa Orientale Italiana (Italian East African Armed Forces Command) and Generale d'Armata Aerea (General of the Air Force), Aosta had about 290,476 local and metropolitan troops (including naval and air force personnel). By 1 August, mobilisation had increased the number to 371,053 troops. On 10 June, the Italian army was organised in three corps and one division commands,

Aosta had two metropolitan divisions, the 40th Infantry Division "Cacciatori d'Africa" and the 65th Infantry Division "Granatieri di Savoia", the Alpini Battalion "Uork Amba" of the 7th Alpini Regiment Alpini (elite mountain troops), a Bersaglieri battalion of motorised infantry, several Blackshirt Milizia Coloniale battalions and smaller units. About 70 per cent of Italian troops were locally recruited Askari. The regular Eritrean battalions and the Regio Corpo Truppe Coloniali (RCTC Royal Corps of Somali Colonial Troops) were among the best Italian units in the AOI and included Eritrean cavalry Penne di Falco (Falcon Feathers). (On one occasion a squadron of horse charged British and Commonwealth troops, throwing small hand grenades from the saddle.) Most colonial troops were recruited, trained and equipped for colonial repression, although the Somali Dubats from the borderlands were useful light infantry and skirmishers. Irregular bande were hardy and mobile, knew the country and were effective scouts and saboteurs, although sometimes confused with Shifta, marauders who plundered and murdered at will.

Once Italy entered the war, a 100-strong company was formed from German residents of East Africa and stranded German sailors. Italian forces in East Africa were equipped with about 3,313 heavy machine-guns, 5,313 machine-guns, 24 M11/39 medium tanks, 39 L3/35 tankettes, 126 armoured cars and 824 guns, twenty-four 20 mm anti-aircraft guns, seventy-one 81 mm mortars and 672,800 rifles. The Italians had little opportunity for reinforcement or supply, leading to severe shortages, especially of ammunition. On occasion, foreign merchant vessels captured by German merchant raiders in the Indian Ocean were brought to Somali ports but their cargoes were not always of much use to the Italian war effort. On 22 November 1940 the Yugoslav steamer Durmitor, captured by the German auxiliary cruiser Atlantis, put in at Warsheikh with a cargo of salt and several hundred prisoners.

The Comando Aeronautica Africa Orientale Italiana (CAAOI) of the Regia Aeronautica (General Pietro Pinna) based in Addis Ababa, had three sector commands corresponding to the land fronts,