What Is International Law?

International law is a set of rules governing relations between states. These rules are often binding and are drawn from a variety of sources, such as treaties, custom, state practice, and judicial decisions.


Since World War II, these agreements have expanded to include laws addressing individual rights and accountability. These laws are called international criminal law.

Sovereignty of States

A core concept in international law is sovereignty, which is the legal right of a state to control its own territory and internal affairs. It is also an obligation of states to respect the sovereign equality of other countries and their inalienable rights. A breach of sovereignty is considered an internationally wrongful act. The emergence of human rights as an issue in international law places limitations on sovereignty because governments must comply with agreed upon principles, which limit their authority to act freely within their borders. Globalization and the growth of supranational institutions further restrict sovereignty.

A state may also exercise its sovereignty outside its borders, but the scope of its power and authority is limited by international law. For example, the UN Charter requires states to refrain from interfering in other states’ internal affairs. In the past, Western states were able to use their supremacy to influence the development of international law and the way it reflects their own interests.

There are two dimensions to the sovereignty of states: the internal and the external. The internal dimension of sovereignty involves the control of a bounded territory by a permanent government with a settled population and a monopoly on force. It is a prerequisite for participation in international organizations and diplomacy on an equal footing with other states. This is reflected in the principle of consent, whereby states cannot impose their will on other states.


A treaty is an official written agreement between states that becomes legally binding on all parties upon its signature. It is typically negotiated between representatives of sovereign states, although it can also include international organizations and other legal persons such as corporations or individuals. A treaty may be “self-executing” and thus enter into force at the moment of its signing; or it may require a specific period of time after which it will become fully effective in accordance with the terms of the treaty. It may also require a specific change in the domestic law of a state party in order to fulfill its obligations under the treaty (i.e. a treaty on the prevention of crimes against humanity).

The law of treaties sets out the procedures for signing, ratification, and entry into force of a treaty. The law also provides that a treaty is considered to be invalid if it was concluded by a State which did not have the full powers to do so or if it was induced to conclude the treaty by the fraudulent conduct of another negotiating state.

If a mistake is discovered in a text of a treaty that has been authenticated, it can be corrected by a procedure known as a proces-verbal. The depositary of the treaty must then communicate the proposed corrections to all signatory and contracting states.

International Organizations

International organizations are multinational groups of states that operate through a system of international treaties. These treaties act as a constitution to set out the agencies, functions, and purposes of the organization. IGOs include the United Nations and its family of related bodies, regional intergovernmental organizations such as the African Union or the North Atlantic Treaty Organization, and transnational corporations that operate across borders.

IGOs have a complex impact on the structure of international law. The privileges and immunities granted to them by their constituent instruments are intended to ensure their independence, and allow for legal accountability through internal tribunals rather than through domestic or international courts. However, the exploitation of these regulatory arbitrages by some IOs can deprive victims of their access to justice in violation of fundamental human rights principles.

In addition, the rules of some IOs may be interpreted as incorporating principles of general international law, and so can be considered part of the legal order of the relevant global community. For example, in granting its members immunity from suit, the Vienna Convention on Diplomatic Relations explicitly references the immunities enjoyed by foreign governments.

The most controversial of the international organizations is probably the European Union, which is a unique form of intergovernmental organisation in that it has been given substantial law-making powers by its members. This is why the EU is often described as sui generis, and it is a major influence on international law.

Conflict Resolution

Achieving a peace agreement between two states is a difficult task, especially when the two parties have a history of conflict and animosity. One way to address this is by identifying the causes of the conflict and working together to find a solution. This can be done through facilitated communication and active listening. During this process, both sides should be allowed to air their grievances and provide feedback. Eventually, it is important to build trust and apologize if necessary.

The behavior of states in conflict and the peace agreements they conclude are impacted by international law. Likewise, the actions of non-state actors in interstate conflict affect the body of state practice that is customary international law.

While the last century’s great wars resulted in setting international rules and institutions that regulated conduct during conflicts and significantly advanced international law, it is increasingly clear that the system needs to take a fresh look at conflict resolution. USIP seeks to develop international legal norms that incentivize and support states, as well as other relevant actors, toward accepting negotiations for peaceful settlement of domestic armed conflicts.