a) Germany declines on declaring unrestricted submarine warfare.
b) Entente runs out of money in April 1917.
c) Kerensky Russia and France forced to ask for an armistice. Britain still wants to continue, but lets their Allies seek armistice terms that don't hurt Britain's strategic position badly.
(armistice terms for France, Germany occupies: Verdun, Toul, Belfort fortresses. France returns all POWs, Germany returns non officer French POWs. Germany allowed economic+diplomatic transit rights on French rail and shipping, France transfers rail rolling stock to Germany.
(armistice terms for Russia, Russia evacuates Turkey+Persia+the bits of Austrian Galacia she holds, Russia returns all Central Powers POWs, Central Powers returns non officer POWs, Germany to receive shipments of grain, oil and cotton from Russians via certain to be repaired rail "ports"). Germany allowed economic+diplomatic transit rights on Russian rail and shipping.
Belgian, Italian, Serbian and Romanian armistices happen shortly after.
Final peace to happen after Britain makes peace.
Britain and Germany remain at war with out any active military fronts except in the Ottoman empire and at sea.
In 1919 with the just completed Baghdad railway through the Tarsus mountains, Germany plans a major offensive to retake Baghdad, Basra, Mecca and the Suez Canal, includes Afghanistan in a war to set India aflame with German support. This small scale war lasts for 10 years.
Peace happens in 1929.