Australia, Canada, New Zealand and South Africa had all achieved Dominion status in the years preceding the First World War. Together they supported Great Britain in waging war on Germany and her Allies. The leader of the Australian Labor Party, Andrew Fisher, stated that Australia would give 'our last man and our last shilling' to the war effort. Dominion forces of the Empire fought in the major theatres of war as well as several 'minor' ones such as Samoa, New Guinea, Cameroon, East Africa and Togoland. At Gallipoli, the fighting experience and losses sustained by the Australians and the New Zealanders helped in forging their national identities, as did the Canadian Corps success at Vimy Ridge on the Western Front. This was not the case with the South African action at Delville Wood. The South African Brigade was comprised of white soldiers only, South African black citizens being barred from a combatant role and only went to France as the South African Native Labour Contingent and were kept in segregated compounds. Other assistance to the war effort included the industrial contribution of Canada who supplied a third of the British Army's munitions in France and Belgium during 1917-1918.

In the Inter-War period the Royal Navy and the Royal Air Force had prominent roles in the Empire with the naval base at Singapore and the internal security role of the RAF in the Middle East and on the North West Frontier. Other Commonwealth fighting units supported the British forces. These included the Royal West African Frontier Force and the King's African Rifles in aid to civil power and the Palestine Police and the Arab Legion supporting the British Army in Palestine. The Army was heavily involved in imperial policing, a third of its men being based in India and garrisons in Egypt, Sudan, Palestine, Singapore, Hong Kong, Shanghai, Jamaica, Malta, Gibraltar and Cyprus.

The Second World War marked both the revival and the decline of the British Empire. India, for example, provided the base for supplies for the Middle East and South East Asian theatres and two and a third million personnel served in the Indian Armed Forces. However after the Fall of Singapore, which severely damaged the prestige of the Empire in South and South East Asia, 130,000 troops surrendered of which 32,000 were Indian. These subsequently made up the majority of the Indian National Army who allied themselves with the Japanese Forces. The INA achieved no military success, but were treated as freedom fighters by Indian nationalists on their return to India after the war. In contrast, the XIV Army, largely composed of Indian Army divisions, was intensely loyal and ultimately very successful against the Japanese in the Battles of Kohima and Imphal and the later reconquest of Burma. British units continued to be supported by forces from the Empire and Dominions. Eighth Army in North Africa was made up of Australian, Indian, South African and New Zealand divisions and, on transferral to Italy, the formation was joined by a Canadian division.

By 1948 British troops had left India and Burma, although British and Commonwealth troops were still involved in the Far East in the Malayan and Borneo Emergencies, with similar insurgencies in Africa such as the Mau Mau Insurgency in Kenya. The Imperial policing experience prior to the Second World War was to prove very useful in this counterinsurgency warfare. The last war involving anachronistic Imperial unity before the end of Empire was in Korea. Here, every self-governing territory in the Commonwealth (except Pakistan and Ceylon) was involved, including a Commonwealth Division. In the Suez Crisis of 1956 much Commonwealth support in military operations was unforthcoming for a variety of political considerations. However, there was still Commonwealth support for British military action as late as the Falklands Conflict in 1982, when the New Zealand's deployment of a frigate permitted British vessels to be used elsewhere.

The Commonwealth's military effort in modern times is an integral part of the remit of the Imperial War Museum and is consequently well represented in the collections of the museum. The art collection includes a number of First World War Australian and Canadian recruitment posters and work by the Second World War official Commonwealth artists. There are good collections of documents from Australian and New Zealand soldiers and officers -particularly for the First World War - and for Canadians in both World Wars. In the case of the Indian Army and the African regiments the material only really covers the experience of the officers. There is excellent material from the 81st (West African) Division in Burma. There are exhibits from Commonwealth forces in both World Wars, including a particularly comprehensive collection of insignia. Film coverage of Commonwealth forces in both World Wars is good, except for the Caribbean contribution, represented only by the film West Indies Calling. The work of the First World War official Australian, New Zealand and Canadian war photographers and the photographs of the official war photographers from all theatres in the Second World War form a significant part of the collections. There is a good research collection of oral history material - particularly interviews with Australians from the Second World War. The museum has a large collection of published material on the Commonwealth during the twentieth century. Generally there is a shortage of material within the Museum's collections for its Commonwealth holdings for the inter-war and post-1945 periods.

For other information on the Commonwealth in twentieth century conflict the following institutions should be contacted: The Australian War Memorial, The Canadian War Museum and the South African War Museum. The National Army Museum at Chelsea is the National Repository for the Indian Army, whose collections are complemented by the official records held by the Oriental and India Office Collections in the British Library. The Public Record Office at Kew and the Liddell Hart Centre for Military Archives at King's College London also have much relevant Commonwealth material.