As soon as Austria threatened Serbia a state of war gripped the world. Germany attacked Belgium and France. Italy broke from the Triple Alliance and joined allies for sake of territorial gains in 1915.Japan joined Allies while Turkey came to side of Central Powers. Even US was drawn into conflict on side of Allies in 1917.There was a tremendous attack of Germany on Paris and an invasion of East Prussia by Russians. Power of defensive developed and there was a rapid elaboration of trench warfare with enormous losses. The third phase was of military deadlock which passed slowly into one of aggression upon combatant population behind fronts by destruction of food supplies and by attacks through air.
Actual warfare ceased in November 1918 when an armistice was signed by both parties. As part of Peace of Paris (1919), separate treaties were drafted and imposed on defeated powers such as Treaty of Versaillies on Germany,treaty of St Germain on Austria,Treaty of Sevres with Turkey etc.The 1919 also saw the foundation of the League of Nations.