History of international law facts for kids

The history of international law looks at how rules between countries have grown and changed over time. Modern international law mostly started in Europe during the Renaissance. It grew alongside the idea of countries being independent and having their own governments. As nations formed, they needed ways to get along and set rules for how they would act towards each other.

But even though modern international law is about 400 years old, some of its ideas come from ancient times. For example, ancient Greek city-states had rules for dealing with each other. Also, the Roman law idea of ius gentium (meaning "law of nations") helped manage interactions between Roman citizens and people from other lands. However, not all parts of the world followed these ideas. In East Asia, for instance, the Emperor of China was seen as supreme, not all states as equal.

Early Rules Between Nations

Basic ideas of international law, like treaties, are very old. One of the earliest known treaties was around 2100 BC. It was an agreement between the rulers of Lagash and Umma, two city-states in Mesopotamia. This agreement, carved on a stone, set a clear border between them.

Around 1000 BC, another important agreement was signed. It was between Ramses II of Egypt and the king of the Hittites. This treaty aimed for "eternal peace and brotherhood." It covered respecting each other's land and forming a way to defend each other.

Ancient Greek Practices

Before Alexander the Great, the ancient Greeks lived in many small states. These states often interacted, both in peace and war. This led to a shared culture that set rules for how they would behave. These rules only applied to interactions among Greek states. But in some ways, their community was similar to today's international community.

Roman Law and Fairness

The Roman Empire didn't really create international law for outside groups. It acted mostly on its own when dealing with lands not yet part of the empire. However, the Romans did create laws for interactions between Roman citizens and foreigners. These laws were called jus gentium. They were different from jus civile, which only applied to Roman citizens.

The jus gentium included ideas of basic fairness. It also linked some rules to a natural, independent "natural law." These ideas of fairness and natural law from jus gentium are still seen in international law today.

Early Islamic Law

Early Islamic law also had rules for how wars should be fought. It covered how to treat prisoners of war under the early Caliphate. These rules are seen as early forms of international humanitarian law. For example, prisoners of war had to be given shelter, food, and clothes. Their cultures had to be respected, and killing or revenge was forbidden. Some of these rules were not written into Western international law until much later. Islamic law set limits on military actions. This included trying to make wars less harsh, guiding how to stop fighting, telling the difference between civilians and soldiers, preventing needless destruction, and caring for the sick and wounded.

Rise of Nation-States

After the fall of the Roman Empire and the breakup of the Holy Roman Empire, Europe had many independent cities, small states, kingdoms, and nations. For the first time, there was a real need for rules of conduct between many different groups. Without a big empire or a main religious leader to guide international dealings, most of Europe looked to Justinian's code of law (from the Roman Empire) and the canon law of the Catholic Church for ideas.

Trade and Maritime Law

International trade was a big reason for creating clear rules between states. Without a code of conduct, there was little to protect trade or merchants from one state acting against another. Countries realized it was in their own best interest to have common international trade rules. This was especially true for rules and customs of maritime law, which deals with the sea.

As trade, exploration, and wars became more complex, the need for common international customs grew. The Hanseatic League, a group of over 150 towns in what is now Germany, Scandinavia, and the Baltic states, created many useful international customs. These helped trade and communication. Italian city-states developed rules for diplomacy as they started sending ambassadors to other capitals. Treaties, which are agreements between governments meant to be binding, became important for protecting business. The terrible Thirty Years' War also led to a strong demand for rules of war that would protect ordinary people.

Hugo Grotius and Modern Law

As international practices, customs, rules, and treaties grew, they became very complex. Several smart people tried to gather them all into organized books. The most important of these was Hugo Grotius. His book, De Jure Belli Ac Pacis Libri Tres, is seen as the starting point for modern international law.

Before Hugo Grotius, most European thinkers believed law was something separate from humans. They thought some laws were made by people, but they always reflected a deeper, natural law. Grotius agreed, but with one key difference. Earlier thinkers believed natural law came from a god. Grotius, however, believed natural law came from a basic, universal reason that all humans share.

Rational Principles of Law

This idea allowed Grotius to suggest several logical principles behind law. He thought law wasn't just given from above, but came from core ideas. Key principles included that promises must be kept, and that if you harm someone, you must make it right. These two ideas have been the basis for much of international law since then.

Besides natural law, Grotius also wrote about international custom, or voluntary law. He stressed the importance of actual practices, customs, and treaties—what countries *do*—instead of just what they *should do*. This way of looking at international law, called positivism, became stronger over time. As nations became the main type of state in Europe, their human-made laws became more important than religious ideas. So, the law of what "is" done became more important than the law of what "ought to be" done.

Peace of Westphalia

The Peace of Westphalia treaties in 1648 were a major turning point. They firmly set the idea of state sovereignty (meaning each country has the right to govern itself without outside interference) as a key part of the international system.

However, the first ideas for independent theories of international law appeared earlier, in Spain, in the 1500s. Important thinkers included the Roman Catholic theologians Francisco de Vitoria and Francisco Suárez. Suárez was especially important because he separated ius inter gentes (law between nations) from ius intra gentes (law within nations). Ius inter gentes is like modern international law.

In 1625, Hugo Grotius wrote the first full book on international law, de iure belli ac pacis. It covered the laws of war and peace. A key part of Grotius's work was that he didn't base international law only on natural law. He also accepted that countries could create binding rules among themselves, called ius voluntarium (voluntary law).

Natural Law and Positivism

Even in the 1600s and 1700s, the idea of natural law as a basis for international law remained strong. Thinkers like Samuel von Pufendorf and Christian Wolff wrote about it. But in the late 1700s, there was a shift towards positivism in international law. Also, the idea that international law could keep peace was challenged. This was because of growing tensions between the major European powers: France, Prussia, Great-Britain, Russia, and Austria.

This struggle between legal rules and political needs is clearly shown in Emer de Vattel's important book, Du Droit des Gens (1758). By the end of the century, Immanuel Kant believed that international law, if it could justify war, no longer served peace. So, in his books Perpetual Peace (1795) and Metaphysics of Morals (1797), he argued for creating a new kind of international law.

After World War I, people tried to create this new international law of peace. The League of Nations was meant to be a key part of this effort, but it failed. The Charter of the United Nations (1945) shows that the old idea of state sovereignty is still central to the law of nations. However, recent studies show that the idea of outlawing war (called ius contra bellum) actually began in the 1800s.

Historians of international law, especially some German authors like Wilhelm Grewe, have divided its history into periods. These include the Spanish era (1494–1648), the French era (1648-1789/1815), the English era (1789/1815-1919), and the American era since 1919. Big peace agreements often mark the transitions between these times. Examples include the treaties of Westphalia (1645–48), Ryswick and Utrecht (1697/1714), Vienna (1814–15), Paris (1919), and San Francisco (the UN Charter, 1945).

The League of Nations

After World War I, just like after the Thirty Years' War, there was a strong demand for rules of warfare. People wanted to protect civilians and stop invasions. The League of Nations, created after the war, tried to stop invasions. It set up a treaty that allowed for economic and military punishments against member states that used "external aggression" to invade other members.

An international court, the Permanent Court of International Justice, was also created. Its job was to settle disagreements between nations without going to war. Many nations also signed treaties agreeing to use international arbitration instead of fighting. However, international crises showed that nations were not yet ready to let outside groups tell them how to run their affairs. Aggression by Germany, Italy, and Japan went unchecked by international law. It took a Second World War to end it.

The Postwar Era

After World War II, just like after World War I and the Thirty Years' War, there was a strong desire to avoid the horrors of war. The idea of the League of Nations was tried again through a new organization, the United Nations.

The time after World War II has been very successful for international law. Countries now cooperate much more often, though not always. Importantly, almost 200 nations are now members of the United Nations. They have willingly agreed to follow its charter. Even the most powerful nations have seen the need for international cooperation. They often seek international agreement before going to war.

International law is not just about how wars are fought. Most rules are about everyday things, like sending mail, trade, shipping, and air travel. Most countries follow these rules routinely because they make life easier for everyone. These rules are rarely argued about. But some international laws are very political and cause heated debates. This includes not only the laws of warfare but also things like fishing rights.

Modern Customary International Law

An important change in modern international law is the idea of "consent." Before World War II, a nation was only bound by a rule if it had formally agreed to it. Or, if it was already following that rule as a custom. Now, simply agreeing to an international practice is enough to be bound by it, even without signing a treaty.

This idea of consent is part of customary international law. It grew from Grotius's positivist approach. Customary international law is basically what states actually *do* (called state practice). Plus, it includes what states *believe* international law requires them to do (called opinio juris).

Customary international law applies to every country. This is true whether they have formally agreed to it or not. At the same time, all countries help create customary international law through their actions and decisions. As new rules appear, countries can accept, reject, or change them. When most countries follow a rule, everyone else will be expected to follow it too. So, doing nothing can mean you are agreeing. Nations that don't act might find themselves bound by an international law that isn't to their advantage.

However, a treaty can overrule customary international law. Because of this, many customary international laws have been formally agreed to through treaties between nations.

Modern Treaty Law

Treaties are basically like contracts between countries. They are agreements where the parties intend to be bound by what they say. If treaties are broken, their power is weakened. This is because there's no guarantee that future promises will be kept. So, nations have a strong reason to take treaties very seriously.

Modern nations use a two-step process to enter into treaties. The first step is signing the treaty. Being a signatory means a country intends to join the agreement. The second step is ratifying the treaty. A country that has ratified a treaty has gone beyond just intending to join. It is now legally bound by the treaty. This is a very important difference and sometimes causes confusion. A nation might sign a treaty for many years without ever ratifying it.

Each country ratifies treaties in its own way. For example, the United States needs two-thirds support from its Senate (the upper part of its legislature) for a treaty to be ratified. Both the president and the legislature must agree. In Canada, however, ratification is an action taken only by the government leader. No approval from parliament is needed before the nation is bound.

Modern treaties are understood and applied according to the 1969 Vienna Convention on the Law of Treaties. This convention is so widely accepted that even nations not officially part of it still follow its rules. The convention's most important rule is that a treaty should be understood by the clear meaning of its words. This should be done within the context of its purpose and with good faith. This prevents many arguments and unnecessary nit-picking. It also encourages treaty writers to clearly state their goals in a non-binding "preamble," which makes interpretation easier.

In today's world, international law is sometimes criticized because it can be hard to enforce its decisions.

See also

• Arbitration § History
• Jus gentium
• Jus naturale
• Third World Approaches to International Law (TWAIL), which offers a different view from the Eurocentric story above.
• Consulate of the Sea international law, from the 13th century, written in Catalonia
• Cities of Refuge, independent city-states in ancient Israel and Judah.