The general principle governing the application and implementation of International humanitarian law is that every state has an obligation to respect and ensure compliance with International humanitarian law in all circumstances.
The term "treaty law" under any circumstances also implies the principle of non-reciprocity, according to which the warring parties must respect their humanitarian obligations, even if these obligations are violated by their opponent. At the most basic level, this reflects the legal principle of the pacta sunt servanda, according to which states must fulfill all the obligations of the agreement to which they are parties. Indeed, a feature of International humanitarian law (IHL) is that a party that fails to comply with its obligations under treaties under international humanitarian law cannot justify the suspension or complete termination of the treaty by any other party. Also, denunciation of treaties of IHL by a party to the conflict may not take effect until the end of any armed conflict that is ongoing at the time of the declaration of denunciation. In addition, military retaliation is allowed to warring parties only in extraordinary circumstances and should never be directed against protected persons or objects. The UN International Court of Justice has even recognized that the obligation to observe and enforce is a general principle of IHL applicable to all armed conflicts and regardless of treaty obligations. At the conceptual level, this obligation has several aspects, namely: (1) the negative obligation to refrain from any intentional violation of IHL; (2) a positive internal commitment to ensure the implementation and enforcement of IHL at the national level; and (3) the positive international obligation of States to exert bilateral or multilateral pressure on other States or Parties to the war to comply with IHL.
In accordance with its duty to adhere to and ensure compliance with IHL, it is clearly the duty of the warring parties and non-warring states to take "all necessary measures" to fulfill their obligations in within its jurisdiction. This may include a wide range of preventive, supervisory and punitive measures, including: (a) national laws and regulations; (b) instructions, military orders and legal advice; (c) preparing and disseminating all relevant information; (d) the establishment of national committees on IHL; (e) technical training; and (f) criminal prosecution.
To ensure compliance with IHL in practice, it must become part of national law. Depending on the national legal system, treaties on IHL may become directly binding under national law (contract law, which is itself enforceable). If treaty law is not applied automatically, states have an international legal obligation to enact relevant legislation to incorporate its provisions into national law. In order to implement certain provisions of the treaties, States may need to adopt new legislation at the national level in order to bring national criminal substantive and procedural law into line with these provisions (nulla points sine lege). Protocol I explicitly requires States to “incorporate into existing law criminal sanctions for those who have committed or ordered others to commit gross violations of IHL” and to ensure that their national law adequately prevents and punishes the misuse of distinctive emblems of the Red Cross, Red Crescent and Red Crystal. There is no formal procedure for "incorporating" the generally accepted provisions of IHL into national law. However, in some states, customary international law can be invoked directly in court proceedings.
In addition to enacting relevant legislation, states and warring parties must also “issue orders and instructions to ensure compliance” with international humanitarian law and “monitor their implementation”. The role of military commanders is particularly important in this. States and Parties to the war must require military commanders to prevent and, if necessary, put an end to violations of IHL committed by members of the armed forces under their command or other persons under their control, and to report such violations by the competent authorities. IHL is a source of erga omnes obligations, namely the legal obligations not only of the warring parties but also of all other states that are parties to a particular treaty or, in the case of customary law, in relation to the international community as a whole. Therefore, all states, regardless of their involvement in the armed conflict, have a legitimate right to demand that a belligerent party comply with IHLand end violations. However, in addition to this discretion, the international aspect of the obligation to respect IHL in all circumstances also means that States have a negative obligation not to encourage the parties to the conflict to commit violations of IHL, as well as a positive obligation. to exert influence in order to stop such violations as far as possible.