What ultimately stopped WWI was the entry of the US.
By 1918, all the other belligerents were war-weary and depleted of manpower. Most were also depleted of industrial capacity. Ludendorff's Spring Offensive was an act of desperation to drive the Allies to the bargaining table before the Americans could arrive in force. It failed on all counts.
By summer of 1918, Americans began arriving at the rate of 10,000 a day, and the Germans never managed to sink even a single American troop ship, so it was obvious they were never going to stop coming. After the German failure at 2nd Marne, Ludendorf admitted Americans were arriving faster that he could kill them, so the Germans had better negotiate and end to the war as fast as possible because the conditions Germany might receive were only going wo worsen as their military position continued to deteriorate.
What started WWI was France’s jealousy of the new kid on the block, when Germany united in 1871. France wanted to be the big dog on the continent, even after Napoleon tried to take over the continent.
So they aligned with Nicky. If not for that alliance, the Germans and Russians would have bashed each others’ brains in, and the rest of the world would have been indifferent as to the outcome.