[Introduction ~causes outbreak modes and events ~ settlement ~ result and aftermath] World War I, one of the most violent human conflicts, was fought between the Allies consisting of France, Russia and Great Britain that backed Serbia, and the Central Powers consisting of Austria-Hungary and Germany. Later twenty other nations such as the United States, China, Italy and Japan joined the Allies and Bulgaria and Ottoman Empire joined the Central Powers. The war was a result of a longtime hostility and tension throughout the European territories. Excessive nationalism developing among the Europeans made them too highly aggressive to their enemies. They made strong and rapid military build-ups, all ‘for the glory and greatness of their nations.’ For instance, Germany alone had 4.2 million soldiers in 1914: Besides their military build-ups at home, they made military alliances sharpening hostility between each other. There was also cutthroat competition among t...