Philosophers such as Grotius, took an interest in the regulation of conflicts well before the first Geneva Convention of 1864 was adopted and developed. In the 18^th century, Jean-Jacques Rousseasu made a major contribution by formulating the basic principle about the development of war between states as:

War is in no way a relationship of man with man but a relationship between states, in which individuals are enemies only by accident; not as men, nor even as citizens, but as soldiers (...). Since the object of war is to destroy the enemy state, it is legitimate to kill the latter’s defenders as long as they are carrying arms; but as soon as they lay them down and surrender, they cease to be enemies or agents of the enemy, and again become mere men, and it is no longer legitimate to take their lives.

In 1899, Fyodor Martens laid down the following principle for cases not covered by humanitarian law: (...) civilians and combatants remain under the protection and authority of the principles of international law derived from established custom, from the principles of humanity, and from the dictates of public conscience. This, also known as the Martens clause, was already considered a standard part of a customary law when it was incorporated in Article1, Paragraph 2, of Additional Protocol I of 1977.

While Rousseau and Martens established principles of humanity, the authors of the St. Petersburg Declaration formulated, both explicitly and implicitly, the principles of distinction, military necessity and prevention of unnecessary suffering, as follows:

 Considering: (...) That the only legitimate object which states should endeavour to accomplish during war is to weaken the military forces of the enemy; That for this purpose it is sufficient to disable the greatest possible number of men;

That this object would be exceeded by the employment of arms which uselessly aggravate the sufferings of disabled men, or render their death inevitable.

The Additional Protocols of 1977 reaffirmed and elaborated on these principles, in particular that of distinction: (...) the parties to the conflict shall at all times distinguish between the civilian population and combatants and between civilian objects and military objectives and accordingly shall direct their operations only against military objectives. (Art. 48, Protocol I; see also Art. 1, Protocol II).

There are also established underlying principles of proportionality that seek to strike a balance between two diverging interests, one dictated by considerations of military need and the other by requirements of humanity when the rights or prohibitions are not absolute. Different writers follow different approach in describing these principles, and for the sake of making a brief explanation of the subject matter we have preferred the one that divides them into seven principles tin reviewing  the rules in the past and present.

The first rule is that persons hors de combat and those who do not take a direct part in hostilities are entitled to respect for their lives and physical and moral integrity. They shall in all circumstances be protected and treated humanely without any adverse distinction. The second fundamental rule provides that it is forbidden to kill or injure an enemy who surrenders or who is hors de combat .The third one is the wounded and seek shall be collected and cared for by the party to the conflict which has them in his power. Protection also covers medical personnel, establishments, transport and material. The emblem of the Red Cross (Red Crescent, Red lion and sun) is a sign of such protection and must be respected.

The fourth rule reads: Captured combatants and civilians under the authority of an adverse party are entitled to respect for their lives, dignity, personal rights and convictions. They shall be protected against all acts of violence and reprisals. They shall have the right to correspond with their families and to receive relief. And fifthly is provided that everyone shall be entitled to benefit from fundamental judicial guarantees. No one shall be held responsible for an act he has not committed.  No one shall be subjected to physical or mental torture, corporal punishment or cruel or degrading treatment.

The sixth one states that parties to a conflict and members of their armed forces do not have an unlimited choice of methods and means of warfare. It is prohibited to employ weapons or methods of warfare of a nature to cause unnecessary losses or excessive suffering. The seventh and the last fundamental rule provides that Parties to a conflict shall at all times distinguish between the civilian population and combatants in order to spare the civilian population and property. Neither the civilian population nor civilian persons shall be the object of attack. Attacks shall be directed solely against military objectives.