What could have happened in WW1 if the common soldier from both sides had just refused to go on? Would the world actually have changed?
I think the world would have to change first before such a thing could happen. Why are you suggesting that Christmas could motivate such a thing?
There was an unofficial Christmas truce. Christmas truce - Wikipedia
I think the OP was asking what if the troops refused to start up again.
Look into the history of the Christmas truces themselves - officers discouraged them out of fear of fraternisation, after the first year they downright forbid them (of course, after a full year of war and hate I daresay the troops themselves might have not been full of merry cheer any more. After two years and gas attacks, “let all the Boches die !”).
And like anything forbidden of the troops, the penalty would quickly be hard time or, if threatening to become widespread, firing squad pour encourager les autres. The army isn’t a democracy.
The bitterest disappointment of early 20th-century socialists was that the common solider didn’t ally with his brother across the line to rebel against the ruling class. Discussions between socialist parties in different countries on the subject of mutually refusing to go to war foundered on two problems: potentially leaving one’s country open to attack by imperialist armies; and that such an agreement would have been tantamount to planned treason, costing the socialists hard-won legitimacy in their home countries.
Even if a substantial number of troops had been willing to say “screw this”, short of an actual revolution there was nothing they could do about it. They couldn’t desert and go home, they would starve if they weren’t kept supplied, and abandoning the war effort without a reciprocal agreement from the other side would have been de facto unilateral surrender. The average soldier fought to defend against enemy attack and to try to keep himself and his friends alive.
Call me a philosopher, but, I believe that if no soldier fought, there would be no war. I can’t guarantee it, of course…
For that to happen, every single person in the world would have to deeply believe that nothing was worth physically fighting for.
Just in case of that, armies have police to curb this impulse. In A Farewell to Arms Hemmingway nailed them as men who get to swagger around in uniforms and shoot people but run no risk of being shot themselves. Sadly, there’s no shortage of applicants for these positions. This results in the paradox in this quote by Stalin: “It takes a brave man to be a coward in the Red Army.”
Germany would have annexed Belgium and a broad swath of northwestern France, and begin preparing for its next victory.