The defence of its Australian colonies was initially the concern of the British government. When the British garrisons were withdrawn from Australia in 1870 each self-governing colonial government had to provide for its own defence. In South Australia the possibility of foreign invasion and violence by convict escapees from other colonies led to the raising of local volunteer forces, which in some cases disbanded when concerns about the perceived threats faded. Each colony separately decided whether to make a contribution to the Empire's forces when requested by Britain, as in the case of the Boxer Uprising, the Sudan War and the South African War.
Since Federation in 1901, national defence has been the responsibility of the Commonwealth. The part played by South Australians in the two world wars, the Korean, Vietnam, Gulf and Iraq Wars, the Malayan Emergency and Indonesian Confrontation, and in the United Nations peacekeeping operations can be traced through the State Library's resources. The Library holds a vast collection of letters, diaries, photographs and personal records written by South Australians who served in the two world wars and other conflicts. A selection of these records has been digitised and is available on this website.