The Russian circular note of 30 December 1898 proposing the programme of the First Hague Peace Conference, suggested as one of the topics "the prohibition of the discharge of any kind of projectile or explosive from balloons or by similar means." Balloons had been used on a small scale in previous wars, and there was much speculation about the future use of aircraft in war. At the First Hague Conference the prohibition was accepted for a period of five years which expired on 4 September 1905. Between the two Hague Conferences progress was made in aerial navigation which induced many states, especially the great Powers, to adopt a more reserved attitude. The Declaration of 1907 was to remain in force until the projected Third Peace Conference.
This Conference never having met, the Declaration of 1907 is still formally in force today. Many of the important States, however, such as France, Germany, Italy, Japan and Russia, did not sign or ratify it. Austria-Hungary signed but did not ratify it. Of the great Powers only Great Britain and the United States ratified the Declaration.
The attempts, in 1907, to adopt a permanent prohibition of the discharge of projectiles from the air led to the insertion in Article 25 of the Hague Regulations on land warfare, which prohibits the attack or bombardment of undefended towns, villages, etc., of the words "by whatever means" in order to cover attack or bombardment from the air.
D.Schindler and J.Toman, The Laws of Armed Conflicts, Martinus Nijhoff Publishers, 1988, pp.202-204.