A world war is a large military conflict between several groups of countries. World War I, also known as the First World War or the Great War and the war to end all wars, pitted Germany, Austria-Hungary, Russia and the Ottoman Empire against the Allied Powers of Great Britain, France, the United States, Canada, Australia and Japan. The war introduced new military technologies and produced unprecedented carnage. In the end, more than 16 million people-soldiers and civilians-died. The war ended with the defeat of the Central Powers and the founding of the League of Nations. Resentment at the onerous terms of the Treaty of Versailles fueled Adolf Hitler’s rise, which led to World War II.

The assassination of Archduke Ferdinand of Austria-Hungary triggered a chain reaction that culminated in the war. However, other major underlying trends also contributed to the start of the world war: imperialism, which allowed countries to extend their influence by controlling territory; and nationalism, which encouraged loyalty based on ethnic or cultural background rather than shared values and interests.

As military technology advanced, countries built larger and more powerful navies and armies. The resulting massed forces clashed at sea and on land. In the Pacific, the US Navy decisively defeats the Japanese fleet at the battle of Midway and then drives the Axis back to Europe with strategic bombing campaigns against German cities. General Allenby retakes Jerusalem weeks ahead of schedule, dealing a blow to Turkish forces.