The declaration of war by Italy on the United Kingdom and France on 10 June 1940 created additional problems for the Middle East Command. In August 1940, the Italians invaded British Somaliland overwhelming the small garrison of one British, two Indian and two African battalions, which was successfully evacuated to Aden.

The build up of British and Dominion troops began with the transfer by sea of the two West African brigades to East Africa, where they joined the two East African brigades. Two infantry divisions were formed in July 1940, the 1 (African) and 2 (African) Divisions (soon redesignated as the 11 (African) and 12 (African) Divisions), each comprising one East African and one West African brigade. The South African Army provided the 1 South African Infantry Division, armoured car units, artillery, engineers and supporting services to East Africa Force.

The build-up of resources in East Africa was bedevilled by the lack of equipment and weapons. It became a campaign of improvisation, with much of the specialist men and materiel being supplied by the South Africans. The Italian forces were large in number, but only a small number of units were well-equipped and well-trained.

The new General Officer Commanding-in-Chief of East Africa Force, Leiutenant General Alan CUNNINGHAM was directed by the Commander-in-Chief of Middle East Command General WAVELL to plan for an offensive to capture Italian East Africa. This was to be coordinated with an advance by the 4 Indian and 5 Indian Division from The Sudan into Eritrea.

The campaign commenced in January 1941, with the three divisions of East Africa Force forcing the Italian Army to retreat. The port of Mogisdishu was captured and then the divisions aimed for the capital of Ethiopia, Addis Ababa, which was entered on 6 April 1941. The main body of the Italian Army surrendered on 19 May 1941, however, some troops held out at Gondar until 27 November 1941.

With the campaign over, East Africa Command was now responsible for the garrison in Ethiopia, including repatriating Italian civilians and guarding prisoners-of-war. There was also the need to blockade French Somaliland until that country agreed to surrender to British forces. East Africa Command was also responsible for the expansion of East African forces, and the campaign in Madagascar in 1942.

By 1944, East Africa Command had sent one infantry division (11 (East Africa) Infantry Division) and two independent brigade groups (22 and 28 (East Africa) Infantry Brigades) to the Far East for operational service in the Burma campaign, and was also still garrisoning Ethiopia, Madagascar and providing reinforcements for the active formations.

During late 1944, the responsibilities for East Africa Command began to decline and in 1945 with the end of the war, the Command transformed onto a peacetime footing, demoblising the returning formations from Burma. The Command continued to function post-war, including during the Kenyan Emergency in the early 1950’s until all the British colonies gained independence from the United Kingdom.