An Irish abbot drafted rules to shield civilians in 697
In 697 the abbot Adomnán of Iona summoned kings and churchmen from across Ireland and Scotland to Birr. There he gave them the Law of the Innocents, which forbade killing women and children in war and destroying churches, one of many early attempts to put limits on combat.
The law of war has two strands. One, known as jus ad bellum, governs when a state may resort to force and includes the crime of aggression; the other, jus in bello or international humanitarian law, governs conduct once fighting starts, covering surrender, prisoners, proportionality and weapons that cause needless suffering. Treaties bind the states that sign them, while unwritten customary rules apply more broadly.
Restraints are ancient. The Code of Hammurabi, around 1750 BC, declared its purpose to stop the strong oppressing the weak. Deuteronomy allowed besiegers to fell only trees that bore no fruit, sparing food sources. Early in the 7th century the first caliph, Abu Bakr, ordered his troops to spare children, women, the elderly, fruit trees, livestock not needed for food, and monks. Augustine of Hippo, against Christian writers who rejected soldiering altogether, set out when war could be morally justified, and medieval movements such as the Peace and Truce of God tried to restrict fighting. Hugo Grotius later sought to write systematic laws of war.
After the Thirty Years' War, Europe entered what has been called a golden age of wartime restraint, lasting nearly three centuries, in which professional armies usually fought for limited aims and left civilians mostly alone. In 1820 Simón Bolívar and the Spanish commander Pablo Morillo signed a treaty to regularise their war, a forerunner of humanitarian law. The Union's Lieber Code during the American Civil War shaped rules for land warfare, and in 1864 twelve countries signed the first Geneva Convention protecting medical crews.
Codification accelerated as hopes grew that arbitration might one day replace war. At the call of Tsar Nicholas II, peace conferences at The Hague between 1899 and 1907 produced detailed conventions. The historian Geoffrey Best saw the years from 1856 to 1909 as the period when these rules enjoyed their greatest prestige, when written treaties replaced reliance on religion and chivalry. After the Second World War, the Nuremberg judgment held that the 1907 Hague rules had become customary law binding even on states that never signed them.
Source: Law of war
