On Anzac Day 1939, 100,000 Australians gathered at cenotaphs and memorials across the country to commemorate the 24th anniversary of the landing at Gallipoli.
Five months later, on September 3, then prime minister Robert Menzies announced Australians would again be sent overseas, to fight in what is now known as World War II.
"Fellow Australians, it is my melancholy duty to inform you officially, that in consequence of a persistence by Germany in her invasion of Poland, Great Britain has declared war upon her and that, as a result, Australia is also at war," Mr Menzies said in his broadcast on national and commercial radio.
"No harder task can fall to the lot of a democratic leader than to make such an announcement."
Australia was part of the British Empire and as such, one of the first countries to declare war on Nazi Germany.
Over the next six years, nearly one million Australian men and women served in what is now known as World War II.
They served in battles against the Axis powers (including Germany, Italy, Hungary, Romania, Slovakia and Bulgaria) in north Africa, the Mediterranean and Europe. In 1941, The Japanese Imperial Navy attacked Pearl Harbour and advanced into South East Asia.
Subsequently, the Allies were also at war with Japan.
For the first time in history, the Australian mainland came under direct enemy attack, when the Japanese bombed Darwin in 1942.
Japanese midget submarines also sailed into Sydney Harbour in May, sinking the HMAS Kutabul which had 21 naval personnel on board.
It was a stark reminder Australia was not immune to enemy attack.
World War II battles in which Australians fought and were killed, including Tobruk, El Alamein, the New Guinea offensives and the Borneo campaign are now etched into our memories.
In all, 39,000 Australians had lost their lives and another 30,000 taken prisoner between 1939-45.
April 25, 1946 drew record crowds at Anzac Day marches across the country. At Martin Place in Sydney 30,000 people gathered to honour the fallen, while in Adelaide 25,000 people joined the march.
There was also a march of those who had served, as well as dignitaries, at the Australian Warm Memorial in Canberra, which had opened on November 11, 1941.