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Wartime works

Seeking a more structured way to play war games, Wells wrote Floor Games (1911) followed by Little Wars (1913), which set out rules for fighting battles with toy soldiers (miniatures). A pacifist prior to the First World War, Wells stated "how much better is this amiable miniature than the real thing". According to Wells, the idea of the game developed from a visit by his friend Jerome K. Jerome. After dinner, Jerome began shooting down toy soldiers with a toy cannon and Wells joined in to compete.

During August 1914, immediately after the outbreak of the First World War, Wells published a number of articles in London newspapers that subsequently appeared as a book entitled The War That Will End War. He coined the expression with the idealistic belief that the result of the war would make a future conflict impossible. Wells blamed the Central Powers for the coming of the war and argued that only the defeat of German militarism could bring about an end to war. Wells used the shorter form of the phrase, " the war to end war ", in In the Fourth Year (1918), in which he noted that the phrase "got into circulation" in the second half of 1914. In fact, it had become one of the most common catchphrases of the war.

In 1918, Wells worked for the British War Propaganda Bureau, also called Wellington House. Wells was also one of fifty-three leading British authors — a number that included Rudyard Kipling, Thomas Hardy and Sir Arthur Conan Doyle — who signed their names to the "Authors' Declaration." This manifesto declared that the German invasion of Belgium had been a brutal crime, and that Britain "could not without dishonour have refused to take part in the present war."