Sources of IHL

silent enim leges inter arma’ (in time of war, law is silent).
Cicero from Pro Milone, 4.11 (52BC)

Despite Cicero’s famous comment, many societies throughout history have attempted to regulate or limit the extent of violence employed during armed conflict.

Examples of ‘humanitarian’ restrictions in war can be found in ancient texts, such as Sun Tzu’s The Art of War, as well as in religious texts from Islam, Judaism, Christianity, and in Buddhist philosophy.

Modern international humanitarian law is found in treaties and customary international law.


Treaties are written international agreements between States, governed by international law. Treaties can go by many names, including conventions, agreements, and instruments; treaties that relate to or attach in some way to previously adopted treaties are often called protocols. Treaties have the advantage of expressly setting out binding obligations for States in their conduct. However, States are often permitted to make reservations to treaties, whereby a State can modify the scope of the legal obligation owed by the State under the treaty. Treaties also require a certain number of States to ratify before the treaty can have legal effect.


Customary international law is a form of law that derives from two elements – State practice and what is known as opinio juris – the belief that the practice is required by law. Identifying custom relies on looking to certain elements including:

  • the degree of consistency and uniformity of the State practice;
  • the generality and duration of the practice; and
  • the interests of specially affected States. 

There is a wealth of treaty law relating to armed conflict. However, the importance of customary international humanitarian law should not be overlooked. Customary international law has the potential to evolve and develop at a faster pace than treaty law, and can bind States where treaty law does not; customary international law thus allows for universal application of certain rules.

Customary international law can also serve to fill in the gaps where the treaty law is insufficient or non-existent – as is the case with non-international armed conflict. Most international humanitarian law treaty rules are considered as having customary status.

Sources of IHL

To identify the sources of IHL is to undertake a historical study of the development of the laws of war. IHL treaties have often been developed in response to State behaviour in specific wars – often leading to the charge that IHL is ‘one war behind reality’.

Battle of Solferino

A Swiss businessman, Henri Dunant, who was travelling through northern Italy, witnessed the aftermath of the June 1859 Battle of Solferino, where tens of thousands of wounded and dying soldiers had been left on the battlefield by their retreating armies. Appalled that no systematic relief was being provided to these soldiers, Dunant rallied the townsfolk of nearby Castiglione to provide water, food, and medical assistance. Upon his return home, Dunant wrote of his experience; his work Un Souvenir de Solferino (A Memory of Solferino) became a best seller. One of Dunant’s suggestions was for the creation of an international body that could coordinate relief measures for the wounded in the armed forces during wartime. In conjunction with a Swiss charitable organisation (the precursor to the International Committee of the Red Cross), Dunant lobbied European governments to implement his suggestions. This advocacy resulted in the European States drafting and adopting what would become the 1864 Geneva Convention.

1864 Geneva Convention

The first multilateral international law treaty on armed conflict was the 1864 Geneva Convention for the Amelioration of the Condition of the Wounded in the Field which provided that soldiers rendered hors de combat due to illness or injury were to be protected and cared for, regardless of their nationality or allegiance. It also provided for the protection of medical and religious personnel; and respect for the execution of their duties in wartime.

Declaration of St Petersburg

Four years later, further development of the law of armed conflict came with the 1868 Declaration of St Petersburg, the first of the modern laws of armed conflict to prohibit the use of a particular weapon of war. The St Petersburg Declaration banned the use of explosive projectiles under ‘400 grammes weight’ designed either to explode on contact with soft tissue, or which were loaded with ‘fulminating or inflammable substances’. (A fulminating substance is one that explodes suddenly and violently if struck or heated). The Declaration of St Petersburg banned the use of such projectiles, determining that:

the progress of civilisation should have the effect of alleviating as much as possible the calamities of war; the only legitimate object which States should endeavour to accomplish during war is to weaken the military forces of the enemy … this object would be exceeded by the employment of arms which uselessly aggravate the sufferings of disabled men, or render their death inevitable; the employment of such arms would, therefore, be contrary to the laws of humanity.

First Hague Peace Conference

Attempts to codify additional rules for armed conflict occurred in the years following the adoption of the St Petersburg Declaration, without success, until 1899, with the convening of the first Hague Peace Conference. The Conference met with the aim of adopting a unified set of regulations regarding the conduct of armed conflict. To that end, three conventions and three declarations relating to the means and methods permissible in armed conflict were drafted and adopted.

These rules would be known as the Hague Regulations of 1899, and included:

  • Convention (I) for the Peaceful Adjustment of International Differences;
  • Convention (II) Regarding the Laws and Customs of War on Land; and
  • Convention (III) for the Adaptation to Maritime Warfare of Principles of Geneva Convention of 1864.

The three Declarations were to prohibit:

  • the launching of projectiles and explosives from balloons or by other similar new methods;
  • the use of projectiles, the only object of which is the diffusion of asphyxiating or deleterious gases; and
  • the use of bullets which expand or flatten easily in the human body, such as bullets with a hard envelope, of which the envelope does not entirely cover the core or is pierced with incisions.

Second Hague Peace Conference

The Conventions and Declarations were revisited at the second Peace Conference at The Hague in 1907, where ten conventions were adopted covering the settlement of international disputes, the laws and customs of war on land, and rules regarding naval warfare – these are known as the Hague Regulations of 1907.

Marten’s Clause

The 1899 Conference also adopted the Martens Clause, a clause adopted to resolve a stalemate at the conference regarding the status of resistance fighters who take up arms against an occupying authority. Named for its author, Russian delegate to the Hague Conference Fyodor von Martens, the clause was a compromise position which decreed that, until a more complete set of laws of armed conflict could be decided upon, the community of nations should not assume the law was silent on matters that were not codified. States were to consider themselves bound by certain minimum fundamental standards of behaviour, as understood by considerations of ‘humanity’ and ‘public conscience’. The Martens Clause was also included in the Preamble to the 1907 Hague Convention IV. The intent of the Clause was to ensure that States did not attempt to argue that the absence of explicit rules on certain situations allowed for unilateral arbitrary action in armed conflict.

1925 Geneva Protocol

The Hague Regulations were the first internationally applicable documents regarding the conduct of parties to an armed conflict. However, the experiences during World Wars I and II provided the impetus for considerable revision and expansion of many aspects of the law of armed conflict. The first revisions and developments came with the adoption of the 1925 Geneva Protocol for the Prohibition of Poisonous Gases and Bacteriological Methods of Warfare, adopted in response to the widespread devastation caused by the use of poisonous gas during the First World War. The Protocol banned the employment of poison gases as well as any kinds of bacteriological warfare.

Geneva Conventions

The next major development came with the adoption, in 1929of two Geneva Conventions, one for the protection of Prisoners of War, and the second on Wounded and Sick in Armies in the Field. These two conventions were eventually replaced in 1949 with four conventions:

  • Geneva Convention (I) for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field;
  • Geneva Convention (II) for the Amelioration of the Condition of Wounded, Sick and Shipwrecked Members of Armed Forces at Sea;
  • Geneva Convention (III) Relative to the Treatment of Prisoners of War; and
  • Geneva Convention (IV) Relative to the Protection of Civilian Persons in Time of War.

These Conventions introduced a raft of new rules for the protection of persons in time of war, including rules for the protection of persons in occupied territory and for the protection of prisoners of war (POWs). The Geneva Conventions have the distinction of being the first multilateral treaty in history to achieve universal ratification; by 2008 every country in the world was a party to the Conventions.

Common Article 3

The Geneva Conventions also introduced what is known as Common Article 3 – the first piece of international law that regulated conduct in non-international armed conflicts. Common Article 3, so called as it is common to all four Conventions, sets down some limited but fundamental principles governing conduct in non-international armed conflicts.

Protection of cultural property

Also adopted soon after the Geneva Conventions was the 1954 Hague Convention for the Protection of Cultural Property in the Event of Armed Conflict. This convention built on a provision included in the 1907 Hague Regulation on the laws of war on law, which provided that ‘all necessary steps must be taken to spare, as far as possible, buildings dedicated to religion, art, science, or charitable purposes [and] historic monuments’. However, the 1954 convention did not include charitable institutions in its protective system.

Additional protocol I

In the years after World War II, the international community underwent some significant geo-political changes. Colonial powers such as France and the United Kingdom were divesting themselves of their colonial holdings in Africa and Asia, sometimes voluntarily, but more often due to insurgent movements engaging in organised armed violence against their colonial masters. By the 1970s, international attention was increasingly focused on these conflicts. These so-called ‘wars of national liberation’ were becoming so widespread that the United Nations General Assembly adopted a number of declarations regarding national liberation wars, and the right of colonial countries to self-determination. The upshot of these resolutions was that wars of national liberation were to be considered equivalent to a conflict between two sovereign States. With this in mind, the international community met to develop and reaffirm the principles of humanitarian law, adopting, in 1977, Additional Protocol I, which elevated ‘wars of national liberation’ from a non-international armed conflict to the stratum of an international armed conflict. Additional Protocol I provides for its application in situations that are deemed to be:

Armed conflicts in which peoples are fighting against colonial domination and alien occupation and against racist regimes in the exercise of their right of self-determination, as enshrined in the Charter of the United Nations and the Declaration on Principles of International Law concerning Friendly Relations and Co-operation among States in accordance with the Charter of the United Nations.

Protocol I also brought about something of a merger between Hague Law and Geneva Law, in that provisions regarding the protection of civilians and participants as well as rules on the means and methods of warfare were combined in the one document.

Additional Protocol II

The increased frequency of non-international armed conflicts in the post-World War II era was also cause for concern. Along with amendments to the international law of armed conflict, changes were also made to the law of non-international armed conflicts, with the adoption of Additional Protocol II. Protocol II applies in:

… all armed conflicts not covered by Article 1… of Protocol I and which take place in the territory of a High Contracting Party between its armed forces and dissident armed forces or other organized armed groups which, under responsible command, exercise such control over a part of its territory as to enable them to carry out sustained and concerted military operations and to implement this Protocol.

Protocol II was designed to develop the law of internal armed conflict beyond the limited concepts outlined in Common Article 3. (Protocol III was adopted in 2005, introducing a new protective emblem – the Red Crystal).

Weapons limitation

From the 1970s onwards, numerous weapons limitation treaties were debated and adopted. The first of these was the 1972 Convention on the Prohibition of the Development, Production and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on their Destruction, which banned the production of chemical and biological weapons. This was followed in 1976 with the Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques (ENMOD), prohibiting the military or other hostile use of environmental modification techniques. In 1980, the Convention on the Prohibition or Restriction on the Use of Certain Conventional Weapons which may be deemed to be Excessively Injurious or Have Indiscriminate Effects was adopted, which sought to place limitations on the use of certain conventional weapons. The Convention contains a number of protocols, which prohibit or limit the use of:

  • weapons that injure by fragments which are not detectable in human body by X-rays (Protocol I);
  • on-detectable anti-personnel mines (Protocol II);
  • incendiary weapons (Protocol III); and
  • laser weapons that cause permanent blindness (Protocol IV).

The fifth protocol to the Conventional Weapons Convention requires parties to the Protocol clear any unexploded ordnance, such as cluster bombs, land mines, and explosive weapons stockpiles, at the cessation of hostilities.

Permissible means of warfare

Additional treaties limiting the permissible means of warfare include the 1993 Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction, and the 1997 Ottawa Convention on the Prohibition of the Use, Stockpiling, Production and Transfer of Anti-Personnel Mines and on their Destruction. The most recent international weapons treaty, the 2008 Cluster Munitions Convention, which banned the use of certain types of cluster munitions (weapons which contain smaller explosive sub-munitions designed to scatter in the air and thus cover a wider area with explosives).