Reasons:
* Alliances: Australia was part of the British Empire and thus bound by its alliances. Britain declared war on Germany on August 4, 1914, after the German invasion of Belgium.
* Nationalism: Many Australians felt a strong sense of patriotism and loyalty to the Empire. They saw the war as an opportunity to prove themselves on the world stage and defend the British way of life.
* Economic interests: Australia had significant trade ties with Britain and the Allies, and the war provided an opportunity to expand these markets.
* Recruitment: The Australian government actively recruited volunteers for the war effort, both from within Australia and from other parts of the Empire.