Strategic bombing during World War I (29 July 1914 – 11 November 1918) was principally carried out by the United Kingdom and France for the Entente Powers and Germany for the Central Powers. All the nations at war eventually engaged in such bombing, and, excepting Rome and Washington, the capital city of each major belligerent was targeted. A multi-national air force to strike at Germany was planned but never materialized. The aerial bombing of cities, intended to destroy the enemy's morale, was introduced by the Germans in the opening days of the war.