International law deals with the relationships between states, or between persons or entities in different states. It sub-divides into "public international law", and "private international law". When used without an adjective, "international law" generally refers to "public international law", and this article concentrates on that meaning.

Traditionally, international law had states as its sole subjects. With the proliferation over the last century of international organizations, they have been recognized as its subjects as well. More recent developments in international human rights law, international humanitarian law and international trade law (e.g. NAFTA Chapter 11 actions) have led to individuals and corporations being increasingly seen as subjects of international law as well, something which goes against the traditional legal orthodoxy. Since international law increasingly governs much more than merely relations between sovereign states, it may be better defined as law decided and enforced at the international, as opposed to national level.

Sources of International Law

International law concerns obligations states expressly and voluntarily accept between themselves in treaties. It also consists of obligations not enshrined in treaties that may be common to all states and arise from custom. Customary law is established by the past consistent behavior of states, and scholarly summaries have traditionally been looked to as persuasive sources for such legal principles in addition to direct evidence of state behavior. Certain customs achieve the binding force of peremptory norms as to include all states with no permissible exceptions. Legal principles common to major domestic law systems may also be invoked to supplement international law when necessary.

Enforcement by States

Apart from a state's natural inclination to uphold certain norms, the force of international law has always come from the pressure that states put upon one another to behave consistently and to honor their obligations. The reality is that many violations of treaty or customary law obligations are overlooked. If addressed, it is almost always purely through diplomacy and the consequences upon an offending state's reputation. Though violations may be common in fact, states will still try to avoid the appearance of having disregarded international obligations.

States may also unilaterally adopt sanctions against one another such as the breaking of economic or diplomatic ties. In limited cases, domestic courts may even render judgment against a foreign state for an injury, though courts are understandably reluctant to do so and typically prefer to leave these issues to heads of state.

States have the right to employ force in self-defense against an offending state that has attacked its territory or political independence. This right is recognized under the United Nations Charter.

Enforcement by International Bodies

In the case that diplomacy is considered inadequate, the United Nations has established the International Court of Justice to render judgments on the breach of a treaty or a legal custom. However, jurisdiction may be had only with consent, and so the court has little power to address a dispute with unwilling parties. A treaty may also provide for specific procedures to resolve a disagreement or address a breach, such as referral to a particular international body (i.e., the ICJ), or the appointment of an arbitration panel.

Violations of the UN Charter may also be raised by the aggrieved state in the General Assembly or brought to the attention of the Security Council. Enforcement measures may include resolutions censoring the offending state, economic sanctions, or even approval of military action if the violation involves the use of force.

Though states (or increasingly, international organizations) are usually the only ones with standing to address a violation of international law, some treaties, such as the International Covenant on Civil and Political Rights have an optional protocol that allows individuals who have had their rights violated by member states to petition the international Human Rights Committee.


Through the ages a code developed for the relations and conduct between nations. Even when nations were at war, envoys were often considered immune to violence.

The first formal attempts in this direction, which over time have developed into the current international law, stem from the era of the Renaissance in Europe.

In the Middle Ages it had been considered the obligation of the Church to mediate in international disputes. In the 16th and 17th centuries the Church gradually lost its direct influence in international affairs, as Catholic and Protestant powers emerged and struggled for dominance and survival. At the beginning of the 17th Century, several generalizations could be made about the political situation:

  1. Self-governing, autonomous states existed.
  2. Almost all of them were governed by monarchies.
    1. England had a constitutional monarchy.
    2. Not all despots were hereditary: the Holy Roman Emperor and the King of Poland were elected.
    3. Switzerland, the Netherlands, and many Italian city-states were republics.
  3. After the Seven Years' War, there was relative stability in Europe for 130 years (until the 1789 French Revolution).
  4. Land, wealth, trading rights, and monopolizing the new lands were the topics of war.

Some people assert that international law developed to deal with the new states arising, others claim that the lack of influence of the Pope and the Catholic church gave rise to the need for new generally-accepted codes.

The Dominican professor Francisco de Vitoria (in Latin Franciscus de Victoria) of theology at the University of Salamanca lectured on the rights of the natives. He did so while Spain was at the height of its power, after the violent Spanish conquest of Peru in 1536. Charles V, Holy Roman Emperor, protested against the friar, but in 1542 new laws put the natives under protection of the Spanish crown. Vitoria is generally recognized as the founder of modern international law.

The French monk Emeric Cruce (1590-1648) came up with the idea of having representatives of all countries meeting in one place to discuss their conflicts so as to avoid war and create more peace. He suggested this in his The New Cyneas (1623), choosing Venice to be the selected city for all of the representatives to meet, and suggested that the Pope should preside over the meeting. Of course, during the Thirty Years' War (1618 - 1648), this was not acceptable to the Protestant nations. He also said that armies should be abolished and called for a world court. Though his call to abolish armies was not taken seriously, Emeric Cruce does deserve his place in history through his foresight that international organizations are crucial to solve international disputes.

Hugo Grotius (1583-1645) was a Dutch humanist and jurist considered central to the development of international law. He became a lawyer when he was 15 years old and got sentenced to life in prison after going against Maurice of Nassau, son of William of Orange in a trial, but he escaped in fled to Paris. In France, he developed his ideas on international law with his Mare Liberum (Latin for "Free seas"), in which he challenged the claims and attempts of England, Spain, and Portugal to rule portions of the oceans and seas. He gained new international fame in 1625 with his book De Jure Belli ac Pacis (The Law of War and Peace), as it became the first definitive text on international law. It was published only two years after The New Cyneas.

Much of Grotius's content drew from the Bible and from classical history. In his work he did not condemn war as only a political tool, considering cases in which war is appropriate. He further developed the just war theory. A just war fits certain criteria:

  1. It can be to repel an invasion.
  2. It can be to punish an insult to God.
  3. There has to be a just cause (one of the two mentioned above).
  4. It has to be declared by the proper authorities.
  5. It must possess moral intention.
  6. It must have a chance of success.
  7. It must abstain from brutal practices.
  8. Its end result must be proportional to the means used.
The statesmen of the time believed no nation could escape war, so they prepared for it.

Thomas Hobbes (1588-1679) was a political philosopher who moved to France after his ideas raised antagonism from Parliament. In France, he tutored the exiled King of Scotland Charles II. His materialistic views alienated the Catholic clergy, so he went back to England, where he lived until his death. In his book the Leviathan (1651), which was a revision of a previous work, he outlined his political philosophy by stating that men are naturally selfishly individualistic and that their fear of a violent death is the principal motive behind their support of an absolute sovereign (this is known as the social contract theory). He believed that the sovereign should be absolute and that a monarchy was the most efficient form of a sovereign leader (he came to this conclusion after living through the English civil war and seeing the problems of Cromwell's "Commonwealth"). He believed that temporal powers should always be above ecclesiastical powers.

King Henry IV's Chief Minister, the Duke of Sully, proposed the founding of an alliance of the European nations that was to meet to arbitrate issues and wage war not between themselves but collectively on the Ottoman Turks, and he called it the Grand Design, but was never established.

Modern International Law has its roots in the 1648 Treaty of Westphalia. International Law continued to develop with the colonization of the New World, the American Revolution, the French Revolution, the Napoleonic Wars, and on into the 20th Century.

After World War I, the nations of the world decided to form an international body. U.S President Woodrow Wilson came up with the idea of a "League of Nations". However, due to political wrangling in the U.S Congress, the United States did not join the League of Nations, which was one of the causes of its demise.

When World War II broke out, the League of Nations was finished. Yet at the same time, the United Nations was being formed. On January 1, 1942, U.S President Franklin D. Roosevelt issued the "Declaration by United Nations" on behalf of 26 nations who had pledged to fight against the Axis powers. Even before the end of the war, representatives of 50 nations met in San Francisco to draw up the charter for an international body to replace the League of Nations. On October 24,1945 , the United Nations officially came into existence, setting a basis for all international law to follow.

See also: nationality, terrorism, environmental agreements, state, territorial integrity, UNIDROIT, international community.