What Is International Law?

What happens if someone breaks the law? They can be arrested, stand trial, and pay a fine or go to prison if found guilty.

What happens if a country breaks a law? The answer there is more complicated. The world doesn't have an equivalent police force, prisons, or way to collect fines from countries that violate international law. That can make holding countries accountable for their actions difficult. 

Scholars and foreign policy practitioners debate the importance and limits of international law. For some, these laws fail to effectively govern. Critics of international law have substantial evidence to back their claims; many governments openly violate their international legal commitments without consequences. But still, others defend the importance of international law, claiming that despite its limitations, international law helps set standards and can help influence global politics in a variety of ways. An international legal code can help empower domestic publics to hold their governments accountable. 

Debates about international law remain ever-important today. Questions loom around how to apply international humanitarian law and the laws of war in relation to the ongoing conflicts in Ukraine and Gaza. Efforts are underway to expand international law to respond to and regulate the rise of artificial intelligence. Attempts to regulate the international system with laws that govern climate are also expanding.

This resource explores the origins of international law, some of the most important international agreements at its core, the reasons countries sometimes break international rules, and the international courts that aim to enforce them. 

Defining international law

International law takes many forms. Some of the most common types of international law are treaties or otherwise formalized agreements. These are voluntary binding agreements between nations aiming to govern the rights and obligations of participating countries. 

However, not all international law is codified. Customary international law also exists, comprising international obligations that arise from established international practices rather than from formal written treaties.

Some of the first international laws emerged centuries ago. For example, the laws of the sea emerged in the 17th century as countries faced a need to regulate their interactions with the expansion of shipping routes. Such laws continued to expand to address a range of other areas, including issues related to human rights, by the turn of the twentieth century. Determined to usher in an era of peace and prosperity following years of violent conflict around the world, global leaders gathered at the Hague—a city in the Netherlands—in 1899 and 1907 to establish the first laws of war and arms control agreements. These laws aimed to help regulate and prevent mass suffering in warfare. 

The League of Nations (founded in 1920) was among the first international organizations dedicated to securing world peace and adjudicating international disputes. Despite treaties and institutions that emerged during this period, the world descended into two calamitous world wars in the first half of the twentieth century. This dealt a devastating blow to the idealistic belief that international law alone can tame violence.

Nevertheless, in the aftermath of World War II, countries sought to ensure the world would never again experience such horrific conflict. In 1945, that effort led to the creation of the United Nations. The United Nations’ founding document—the UN Charter—laid out rules whereby countries agreed to uphold human rights, respect borders, and settle disputes through negotiation and arbitration rather than conflict. Of course, that agreement hasn’t always worked out, and conflicts still occur—but so far another world war has been avoided.

The UN Charter is not the single rule book for international law. Since World War II, countries have signed numerous agreements on everything from nuclear proliferation, trade, fishing rights, climate change, outer space, the treatment of diplomats, and the rules of war. That body of rules and regulations is collectively known as international law.

What is International Humanitarian Law? What are the Laws of War?

Special international laws exist that aim to regulate wars and conflicts through a collection of agreements. This collection —known as international humanitarian law and the laws of war— aims to regulate the actions of parties engaged in conflict (also known as “jus in bello”, in Latin), and to regulate when parties can lawfully use force against another state (“jus ad bellum”). 

These laws aim primarily to prevent war and conflict. The United Nations Charter prohibits the use of military force with two exceptions: in cases of self-defense and in cases where force is authorized by the UN Security Council. 

If war does break out, international humanitarian law includes a set of rules that seek to limit its impacts on civilians. These principles are codified in the Geneva Conventions of 1949, which has been ratified by 196 countries. Additional protocols have developed over time on specific issues. Specifically, the 1993 Chemical Weapons Convention and the 2000 Optional Protocol to the Convention on the Rights of the Child on the involvement of children in armed conflict represent two treaties that protect civilians during war. Many provisions of international humanitarian law are today accepted as customary international law, meaning they bind all governments.

International principles under the laws of armed conflict include:

• Military necessity: military actions must be necessary; 
• Distinction: they must distinguish between civilians and legitimate military targets (this does not mean that civilian casualties cannot occur, but that they should not be the intended target);
• Proportionality: they must be proportionate, avoiding to the extent possible incidental harm under the principles of self-defense; 
• Humanity: they must avoid unnecessary suffering.

The application of these laws in practice has been difficult. It remains debated how these laws apply to non-state actors. Additionally, principles like proportionality and distinction are difficult to interpret in practice when civilians and military actors are difficult to physically separate. Despite challenges, aspects of international humanitarian law have been successfully applied in some cases. In 2014, for example, international legal principles around humanitarian protection helped facilitate the safe passage for some civilians in South Sudan to flee violence.

Unfortunately, however, many challenges to the implementation of these laws remain, as conflicts and civilian suffering today are commonplace. Concerns are visible about potential breaches of these principles in a range of conflicts —from Sudan, to Ukraine, to Yemen, and beyond.

Why do countries violate international law?

Ordinary citizens can’t simply pick and choose the laws that apply to them. Imagine someone agreeing not to commit murder but saying laws about robbery don’t apply to them.

International law, on the other hand, is based on voluntary buy-in. That means countries get to choose the laws that apply to them. If a government refuses to follow the latest climate accord, there’s little anyone else can do to hold that government accountable. But sometimes, those laws can help mobilize domestic groups that work to hold their governments to account. International law can encourage governments to sign new agreements that adhere to evolving standards.

Countries do not follow certain international laws for several reasons. Sometimes governments believe that international laws clash with their national interests. For example, North Korea withdrew from a treaty prohibiting nuclear weapons in 2003 because it claimed that acquiring nuclear weapons was necessary for its defense. Few, if any, instances exist in which a country would sacrifice its national interest to abide by international laws.

In other instances, countries argue that certain international laws violate their sovereignty—the principle that guarantees countries get to control what happens within their borders. The European Court of Human Rights (ECHR) has repeatedly convicted Russia of discriminating against the LGBTQ+ community. However, despite its conviction and condemnation the Russian government refuses to change its laws. The Kremlin contends that an international court should not determine national laws that Russian citizens have not agreed to. In the United States, the Senate has repeatedly refused to ratify the UN Convention on the Law of the Sea because it believes the pact infringes on U.S. sovereignty. Still, the United States criticizes China for violating the accord.

Other countries cite discrimination as a reason for not following particular laws. The African Union—a regional political forum—encouraged its members to withdraw from the International Criminal Court (ICC), arguing that the court unfairly targets African countries in its human rights cases. Indeed, since the ICC’s founding in 2002, forty-four of the people indicted by the court have been African nationals. The ICC’s indictment of Russian President Vladimir Putin in 2023 was an unprecedented case and the first outside of Africa.

The ICC is one of several courts that adjudicate international legal disputes.

Let’s explore some of the world’s most prominent courts and see where they succeed and struggle in enforcing their rulings.

What is the International Court of Justice?

The International Court of Justice (ICJ), sometimes known as the World Court, is the official court of the United Nations. Headquartered in The Hague, the ICJ’s judges are elected by the UN General Assembly and Security Council. ICJ judges are responsible for resolving legal disputes between the United Nations’ 193 members on issues related to property rights, force, and diplomatic relations, among other issues.

The court has proved successful in resolving border disputes. In the 1990s, Cameroon and Nigeria clashed over Bakassi, a peninsula in the Gulf of Guinea that both countries claimed as their own. The two countries brought their dispute to the ICJ, which ruled in 2002 that Bakassi belonged to Cameroon. After several more years of UN-facilitated negotiations, Nigeria transferred control of the peninsula to Cameroon in 2008. Nevertheless, the world’s most heated territorial disputes are never brought before the ICJ, as neither party would risk losing its case.

The ICJ is also not always able to enforce its rulings. In 2003, the UN General Assembly asked the court to decide whether Israel’s construction of a wall alongside the occupied West Bank violated international law. In just months—a surprisingly quick decision for a court that usually takes years to issue rulings—the ICJ declared the wall was illegal and ordered Israel to stop construction. However, the Israeli government ignored the court’s decision and completed the wall. Israel claimed that additional border security was necessary for defense, questioning the effectiveness of the international court. 

When countries disregard ICJ rulings, the court can ask the UN Security Council to determine the consequences. In the case of the wall, however, the United States—a permanent member of the UN Security Council with the power to block any resolution—sided with Israel, shielding the country from any repercussions for its actions.
 

What is the International Criminal Court?

The ICC is an independent court, also headquartered in The Hague, that is responsible for trying individuals accused of the most egregious human rights violations.

Despite that mandate, the ICC lacks serious enforcement powers, which severely limits its effectiveness. Since the court’s founding in 2002, it has tried thirty-one cases —all of which have involved individuals from Africa. Of these cases, only ten have resulted in convictions. The ICC currently has issued a warrant against Russian President Vladamir Putin alongside another member of his government for crimes against children in Ukraine. However, Russia does not formally recognize the court and refuses to adhere to the warrant.

Given the absence of a global police force, the ICC struggles to bring individuals to trial. Former Sudanese President Omar al-Bashir has avoided standing trial for genocide, war crimes, and crimes against humanity since the ICC first issued a warrant for his arrest in 2006. Only because a 2019 revolution ousted Bashir from power does he now face the possibility of being turned over to the ICC.

Additionally, governments can simply withdraw from the ICC if they are under investigation—Burundi and the Philippines have done just that in recent years. Nothing compels countries to join the ICC in the first place. Although every UN member is subject to the ICJ, only 124 countries have signed on to the Rome Statute, the ICC’s founding document. Notable absences include the United States, China, India, and Russia.
 

The United States even passed a law in 2002 that prohibits its allies from handing American citizens over to the court for prosecution. When the ICC opened an investigation in 2020 into alleged American war crimes in Afghanistan, the White House imposed sanctions on ICC personnel and prohibited their entry into the United States. Nonetheless, the United States has used its position on the UN Security Council to have the ICC investigate individuals. Most notably, the United States had the ICC investigate former Libyan dictator Muammar al-Qaddafi.

What is the European Court of Human Rights?

Founded in 1959, the ECHR is a regional court with members including Russia, Turkey, the countries of the European Union, and several others. Its mission is to uphold the European Convention on Human Rights.

The ECHR is a relatively fast-moving court that adjudicates disputes between countries and hears cases brought by individuals, companies, and nongovernmental organizations. Its landmark judgments have advanced the rights of minority groups within its member countries. Most notably, the ECHR’s 1988 ruling paved the way for Ireland’s decriminalization of homosexuality.

Still, like other international courts, the ECHR faces enforcement challenges. Russia has ignored several ECHR rulings, claiming they violate the country’s sovereignty. The Kremlin is not alone in its ignorance of the ECHR. Member countries have failed to implement thousands of the ECHR’s rulings.

Nevertheless, the ECHR is an example for similar regional human rights courts around the world. The ECHR inspired the establishment of the Inter-American Court of Human Rights and the African Court of Human and Peoples’ Rights.

Do all international courts face enforcement challenges? 

In addition to the ICJ, ICC, and ECHR, dozens of courts and tribunals work to enforce international law. Some focus on particular regions, while others cover the entire globe; some tackle a wide range of issues, while others hear cases related to specific topics like trade, nuclear energy, or maritime disputes.

One commonality between those courts is the challenge of holding offenders accountable for their actions. Take the International Tribunal for the Law of the Sea. In 2016, the court ruled that China’s territorial claims to the highly contested South China Sea had no basis in international law. Despite that ruling, China has continued to militarize the region. Beijing has faced few, if any, consequences for its actions.

International law has facilitated negotiation and cooperation among countries on issues of global importance like trade and climate change. However, those agreements have their limitations. Without strong enforcement mechanisms, most international laws and related international courts face continued hurdles.