I know it's a bit of a hypothetical question but every ANZAC Day I hear things like "ANZACs were fighting for our way of life". I feel like this statement needs a bit more evidence to support it. It makes me wonder if Germany would've even cared about Australia geographically, seeing as it is so far away and had so few people in it.
The Germans had territory in the Southwest Pacific, notably Nauru and Kaiser Wilhelm's Land, and there were German cruisers that operated in the Indian and Pacific oceans, wreaking a fair amount of havoc in the first months of the War. British, Indian and ANZAC forces had largely occupied those German territories by 1915, the Japanese having done the same to the German territories in China and around the Marianas and Marshalls.
Essentially no, Australia was never under threat of invasion or occupation by Germany, and certainly NOT the Ottomans. The logistical difficulties that ruled out Japanese invasion in the Second World War DEFINITELY ruled out German invasion in the first.
That said if Britain were to lose the war, and lose badly, where would that leave Australia and New Zealand? They very much relied on Britain for defence, and Britain was a vital economic partner; what if the Empire were struck a heavy, perhaps crippling blow? A defeat of the Entente on the continent (very much a prospect in 1914 AND 1918), allowing the Germans to lay claim to more of Africa and realize their ambitions of Mitteleuropa (German hegemony of the continent), would have left Britain in a dangerous position, and the strains that defeat would have placed on the UK domestically would certainly have had repercussions for the Empire as a whole, of which Australia and New Zealand were a part.
This next bit is lifted from an earlier question I answered about the ANZACS:
However, one must ask oneself why they were fighting. Britain could not standby and allow Germany to exert hegemony over the continent, the High Seas Fleet resting in the Channel ports like a gun pointed at Britain's head. The Dominions relied on Britain for security and economic enterprises, and any threat to Britain was a threat to that empire of which they were a part. This was more pressing for the Aussies and the Kiwis, in light of German possessions in Samoa, the Mariannas and Marshalls, and Kaiser Wilhelm's Land, and the rising power of Japan.
As for the continent, was it not right for Belgium to be able to decide it's future, to remain an independent state and not be partially annexed or made an economic vassal as the Germans intended? How about the French? Was it not right to prevent the Germans from subjugating that country, the home of millions of 'Poilus', fellow soldiers of the French Army?
There's an Australian Historian that I recommend you look into; he died years ago, but his name was Trevor Wilson. He was no defender of the Generals, as his and his colleague Robin Prior's books on the Somme and Passchendaele can attest! In 1986, he published one of the best accounts of the British experience in WWI I've ever read, called 'Myriad Faces of War'. In the final section he asked that, if the First World War cannot apparently be dubbed a 'good war', unlike WWII, can it not at least be considered one of 'Freedom's Battles'? Would the democracies/mostly democracies of Britain, France, Italy and America, even the peoples of Russia, not pay a terrible forfeit in the event of a Central Powers Victory? Would not Democracy in Europe have been greatly curtailed, even more so than it was, by a triumphant Kaiserreich? Was there REALLY so little at stake, as most people assume?
Food for thought! :) I'll leave you with the final passage of his book, which references Field-Marshall Haig's 'Backs to the Wall' despatch, posted below:
"This might be dismissed as the empty rhetoric of an impoverished command. Yet there are grounds for not doing so. For somewhat earlier in the same crisis an identical view was being expressed in a notably different quarter. A passage in the radical periodical the Nation, quoted on a previous occasion, deserves repetition here. Massingham wrote:
In the full brunt of the German assault on France, the true character of the war stands revealed. Vain projects of imperialism obscured it, and vainer diversions of strategy. Both have disappeared... the war emerges from these mists not as a war of adventure, but morally and physically as a war of defence.... The war was not for colonies, Imperial Ambitions, or a balance of power. It was to teach militarism a lesson of restraint.
What seems of particular note is the congruity between Haig's affirmation that the issue at stake was 'the safety of our homes and the freedom of mankind' and Massingham's characterization of the war as a 'war of defence', a war to 'teach militarism a lesson of restraint'. In short, despite their great differences in background and outlook, each was prepared to claim that this was in truth one of freedom's battles.
Perhaps in so perceiving the conflict, the traditionalist Field-Marshall and the radical journalist were both deluded.
Perhaps, on the other hand, they were not."
I'd argue that both wars, as terrible and dreadful for humanity as they were, were wars that Australia could not stay aloof of; but that's, like, my opinion, MAN! :) I had a great uncle in the British Army who was killed at Gallipoli, 3 more and my great grandfather that served in the British Cavalry on the Western Front, so I'll admit that WWI is a topic of particular meaning to me at least.