International law, which consists of the treaties and agreements nations sign with one another, rules of war, the laws of the sea, economics, diplomacy, environmental and human rights issues, and other international institutions and organizations, shapes cooperation on international concerns, ensures accountability and justice, and settles disputes peacefully. Most of this law is not written down, but rather reflects patterns of national behavior over time that have developed into international legal obligations. Because of the mutual respect and understanding that a breach in any concept of international law might result in economic or even military retaliation, most nations accept and follow this body of law.

For example, by signing a treaty, a country agrees to prosecute alleged perpetrators of genocide and other crimes before an international court. The ICC also requires countries to make their citizens aware of the international criminal tribunal’s jurisdiction and ensure that prisoners have access to an effective remedy, such as amnesty, pardon, or commutation of death sentences.

In the aftermath of World War II, countries sought to ensure that such a horrible conflict never occurred again, and they built this system of rules that is now known as international law. It hasn’t always worked, but the resulting global rules and institutions have helped to ensure that the world’s people can live in peace and prosperity. International law continues to expand, as new global challenges, such as cybersecurity, arise. These 100 Ways illustrate that international law penetrates more deeply and broadly into our lives than is often recognized.