The world’s first global conflict introduced the world to horrific trench warfare and lethal new technologies such as poison gas. It claimed the lives of more than 16 million military and civilians and reshaped the map of Europe, destroying the sprawling Russian, Austro-Hungarian, and Ottoman empires and creating new ones.

Amid rising diplomatic tension between the European great powers, a Bosnian Serb named Gavrilo Princip assassinated Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, on 28 June 1914. Austria-Hungary blamed Serbia for the assassination, and enlisted Germany’s support in a war that soon spread across south-east Europe. Russia’s support of Serbia drew in the United Kingdom, which was bound by its treaty obligations to defend Belgium’s neutrality and feared Germany’s domination of Europe, and on 4 August the Western Front opened for the first time.

People across the world responded with unity and purpose. Millions of young men showed up at recruiting centers to volunteer for service. In Britain alone, 2.6 million men did so. Women also volunteered to help the military effort as nurse aides, canteen workers, and other clerical positions. They purchased war bonds and savings certificates, planted victory gardens when food rationing began, and helped house troops or refugees.

By the end of the war, Allied forces controlled greater demographic, industrial and military resources than the Central Powers. Despite this, the peace settlement of 1919 imposed various restrictions on the victorious Allied powers, including the reduction of their territorial holdings and their access to ocean trade. These limitations contributed to the rise of aggressive nationalism in Japan and Germany, which sought to reverse the terms of the Versailles Treaty and reassert their imperial dominance of Asia and the European continent.