I've started watching the amazing YouTube series "The Great War", and am up to November 1914. My question is based on my knowledge from that series, so hopefully it's accurate.
The war very quickly went in a direction none of the leaders had anticipated nor wanted. Instead of a quick victory, each side is already losing millions of men and it is becoming accepted that this will be a very long war.
Given that the war was not triggered by an existential threat to anyone except Serbia, it seems to me that at this point it would make sense to start having multi-party peace talks.
Only Germany had really been spoiling for a fight for quasi-existential reasons, fearing that Russia would catch up industrially in a few years and pose a threat, hence the desire to beat them down now. But given the discovery that the nature of warfare at the time was such that defense has the advantage, due to the advent of machine guns, it seems that this might not have been a goal worth prosecuting such a costly war for.
So if Germany and Russia had been willing to back off to previous borders and made peace, then the Austrians would have had to accept a peace with Russia as well due to their heavy losses and lack of German support. Without Russia to fight, Germany had no reason to continue invading France, and if they had backed off presumably France and the UK would have accepted peace as well. With all this chaos gone, the Ottomans would also presumably have looked for peace with Russia too.
So lots of people lose some face, but millions of lives are saved.
Why did something like this not happen?
https://www.reddit.com/r/AskHistorians/comments/3365de/peace_initiatives_during_wwi/
Similar answers I've given.
Here's the thing; a whole lot of people didn't believe that the stalemate on the Western Front was actually going to be as intractable as it was. Armies had always built field works and other shelter for armies in the field, and trenches were familiar to European warfare since the 1700s, and even before. There had been periods of the American Civil War and of the Russo-Japanese War that had come to temporary stalemate, but mobile operations had eventually resumed.
The Austrians were intent on crushing the Serbs, and as their Army was gutted by the 1914 fighting, there was little chance of the Empire surviving UNLESS they were victorious. The Germans had an opportunity here to 'break the encirclement', crushing the French and weakening the Russians (hence the September Programme of 1914). The French had an invading Army on their home soil that was going no where, the British were facing the spectre of German hegemony on the continent, and the Russians were ACTUALLY making progress, while at the same time were faced with a German Empire that viewed them as an existential threat, and would back It's Ally to the Hilt.
Above all, many thousands are dead, and the threats that all the powers face in Dec. 1914, as I've shown, is greater not less than they faced before. I think the question that should be asked is HOW could they have made peace?
To elaborate on your assertion that there were no "existential threats". The Austro-Hungarians are clearly aware that their interests are opposed by Russia, and that the Serbs intend to raise dissent amongst the South Slav peoples of the Empire. The Germans believe, not without some reason, that they are encircled by hostile powers, and that the balance is slipping. When the Russians mobilize, they seize the opportunity to remove the threats on their borders. The French have a pretty existential threat, they have an enemy sending their army into their country, taking over the area where much of France's industrial resources are, and aren't intent on leaving; I'd say that's a pretty big threat! The Belgians and the Serbs are in similar situations, knowing that if they lose this war, their futures are bleak to say the least. As to the British, the Balance of Power was an article of faith to English/British governance since the 1500s. No one power must dominate the continent, and they should especially not have control of the low countries and the Pas De Calais. The Germans parking 1.4 million men in that exact area is the most serious threat Britain has faced since Bonaparte, and they intervene in Belgium in 1914 to avoid the situation they will face in 1940: staring across the Channel at a hostile power with dominance of the continent. All of these are clear threats, which the belligerents acknowledged at the time, and drove them to fight on, as terrible as that may be.
At the very least, I think David Stevenson's quote is especially apt:
as a contemporary caricaturist pointed out, the opposing leaders found themselves like so many Macbeths, 'in blood stept in so far that should I wade no more, returning were as tedious as go o'er'.'