Treaty of London (1915)

Date: April 26, 1915 • Location: Rome, Italy

This milestone marked the outbreak and beginning of this historic period, which spanned 1915–1918.

First World War: Britain, France and Russia signed a secret treaty promising territory to Italy if it joined the war on their side.

World War I, or the First World War, also known as the Great War, was a global conflict between two coalitions: the Allies and the Central Powers. One of the deadliest conflicts in history, World War I caused 15 to 22 million deaths, including those resulting from war crimes and genocides. The war also contributed to the spread of the Spanish flu pandemic. The conflict saw important developments in weaponry, including machine guns, artillery, aircraft, chemical weapons, and tanks.