The United Kingdom was a leading Allied Power during the First World War of 1914–1918. They fought against the Central Powers, mainly Germany. The armed forces were greatly expanded and reorganised—the war marked the founding of the Royal Air Force. The highly controversial introduction, in January 1916, of conscription for the first time in British history followed the raising of one of the largest all-volunteer armies in history, known as Kitchener's Army, of more than 2,000,000 men. The outbreak of war was a socially unifying event. Enthusiasm was widespread in 1914, and was similar to that across Europe.

Charles Frederick Gurney Masterman PC MP was a British radical Liberal Party politician, intellectual and man of letters. He worked closely with such Liberal leaders as David Lloyd George and Winston Churchill in designing social welfare projects, including the National Insurance Act 1911. During the First World War he played a central role in the main government propaganda agency.