Western Front-Stalemate until America arrived with fresh troops and pushed Germany back in the Meuse-Argonne Offensive.
Italians/Hungarians-Italian defeat at the battle of Caporetto led to an Italian counterattack and defeated the Austro-Hungarian Empire.
Russians-Russian Revolution allowed Germany and Austria-Hungary to focus more on Italy and the other Allies.
Africa-Defeat at Gallipoli restored Ottoman morale. Eventual attack on the Al-Faw Peninsula and occupation of the Suez Canal by British forces destroyed the empire.