On this day 125 years ago, on July 9, 1900 (June 13, 1900 in the lunar calendar), the Australian colonies formed a federation. On July 9, 1900, the Australian colonies formed a federation. The British Parliament accepted the Australian Commonwealth Act, uniting several Australian colonies, including New South Wales, South Australia, Queensland, Tasmania, Victoria and Western Australia, under the rule of a federal government. European and American expansion in the Pacific prompted the six colonies to resolve their differences and form a common defense system.