From the Australian Government Department of Veterans’ Affairs website:
The Anzac tradition—the ideals of courage, endurance and mateship that are still relevant today—was established on 25 April 1915 when the Australian and New Zealand Army Corps landed on the Gallipoli Peninsula. It was the start of a campaign that lasted eight months and resulted in some 25,000 Australian casualties, including 8,700 who were killed or died of wounds or disease. The men who served on the Gallipoli Peninsula created a legend, adding the word ‘Anzac’ to our vocabulary and creating the notion of the Anzac spirit.
In 1916, the first anniversary of the landing was observed in Australia, New Zealand and England and by troops in Egypt. That year, 25 April was officially named ‘Anzac Day’ by the Acting Prime Minister, George Pearce. By the 1920s, Anzac Day ceremonies were held throughout Australia. All States had designated Anzac Day as a public holiday. In the 1940s, Second World War veterans joined parades around the country. In the ensuing decades, returned servicemen and women from the conflicts in Korea, Malaya, Indonesia, Vietnam and Iraq, veterans from allied countries and peacekeepers joined the parades.
During the 1960s and 1970s, the number of people attending the ceremonies fell as Australians questioned the relevance of Anzac Day. However, in the 1990s there was a resurgence of interest in Anzac Day, with attendances, particularly by young people, increasing across Australia and with many making the pilgrimage to the Gallipoli Peninsula to attend the Dawn Service.