The Declaration of Saint Petersburg is the first formal agreement prohibiting the use of certain weapons in war. It had its origin in the invention, in 1863, by Russian military authorities of a bullet which exploded on contact with hard substance and whose primary object was to blow up ammunition wagons. In 1867 the projectile was so modified as to explode on contact with a soft substance. As such the bullet would have been an inhuman instrument of war, the Russian Government, unwilling to use the bullet itself or to allow another country to take advantage of it, suggested that the use of the bullet be prohibited by international agreement. The Declaration to that effect adopted in 1868, which has the force of law, confirms the customary rule according to which the use of arms, projectiles and material of a nature to cause unnecessary suffering is prohibited. This rule was later on laid down in Article 23 (e) of the Hague Regulations on land warfare of 1899 an 1907. The Declaration of Saint Petersburg prompted the adoption of further declarations of a similar nature at the two Hague Peace Conferences of 1899 and 1907. The Hague Declarations relating to the discharge of projectiles and explosives from balloons, the use of asphyxiating gases and the use of expanding bullets refer in their preambles to the Declaration of Saint Petersburg.