What exactly is international law?

The notion that sovereign states would voluntarily constrain their actions according to mutually agreed-upon rules may sound somewhat counterintuitive. Yet international law, while lacking the same enforcement mechanisms as domestic legal systems, has emerged as important framework governing relations between nations. Its effectiveness relies not on police or prisons, but on something more subtle: the states' pragmatic self-interest.

The modern system of international law traces its origins to the 1648 Peace of Westphalia, which established the principle of state sovereignty. But its roots run deeper, to ancient civilizations. The Mesopotamian city-states of Lagash and Umma signed one of the earliest known treaties around 3100 BCE. The Romans developed the concept of jus gentium—the "law of nations"—to govern relations between foreigners and Roman citizens. These early frameworks laid the groundwork for today's more complex international legal order.

Unlike domestic law, international law operates largely through consent. No global legislature exists to pass binding laws, nor is there a comprehensive system of courts with universal jurisdiction. The International Court of Justice (ICJ) can only hear cases when states agree to its authority. Even the UN Security Council, while able to authorize sanctions or military action, requires consensus among its permanent members—a high bar that has often prevented decisive action due to the vetoes of one or more members. The UN General Assembly can only make recommendations such as the 1947 Partition of Palestine Plan which was only a suggestion which was rejected by the Arab states and thus never came into force by means of a signed treaty.

So, what gives international law its force? The answer lies in reciprocity and reputation. States generally follow international rules because they expect others to do likewise by creating stability through credibility that benefits all parties. Breaking international law carries diplomatic and economic costs—states that develop a reputation for violating agreements find fewer partners willing to deal with them. As one scholar noted, "consistent rule violations would jeopardize the value that the system brings to the community of states." If one state consistently acts unpredictable other states are hesitant to enter into agreements with them.

The sources of international law are hierarchical. Treaties—explicit agreements between states—sit at the top. Below these are customary international law (consistent state practices accepted as legally binding) and general principles of law recognized by most nations. Judicial decisions and scholarly writings serve as subsidiary sources. Some norms, like the prohibition on genocide, are considered so fundamental that they are binding on all states regardless of explicit agreement.

The scope of international law has expanded dramatically since World War II. What began primarily as rules governing diplomatic relations and warfare now encompasses human rights, trade, environmental protection, and more. The proliferation of international organizations—from the World Trade Organization to the International Criminal Court—has created new mechanisms for developing and implementing international rules.

Critics argue that international law is merely "politics by other means," pointing to instances where powerful states ignore inconvenient obligations. The United States' withdrawal from various treaties and Russia's violations of international law in Ukraine lend credence to such skepticism. Yet even these examples demonstrate international law's influence—states typically try to justify their actions within legal frameworks rather than reject the system entirely.

The rise of non-state actors has complicated matters. Multinational corporations and NGOs now wield significant influence in international affairs. International law, governing conflicts between different national legal systems, has grown increasingly important in our globalized economy. The traditional view of international law as purely relations between states has become outdated.

Looking ahead, international law faces several challenges. Terrorism, cyber warfare, and artificial intelligence raise novel legal questions that existing frameworks struggle to address. Rising nationalism and growing great-power competition through both “Eurasianism” and “Islamistism” tend to undermine multilateral cooperation because the system's consensual nature makes rapid adaptation difficult.

Yet international law's fundamental value proposition remains strong. In an interconnected world, states need predictable rules to manage their relations. While imperfect, international law provides a language and framework for resolving disputes peacefully. Its effectiveness may rely more on carrots than sticks, but that makes it no less real or important. A good example is the 2006 UN Security Council Resolution which is only now being fully implemented by agreement of relevant parties with a resulting cease fire between Israel and Hezbollah.

Another good example is the 50-year success if the UN Security Council Resolution 350 that emerged in the aftermath of the 1973 Yom Kippur War which proved itself  a vital mechanism for regional stability.  The United Nations Disengagement Observer Force, (UNDOF) represents one of the UN's most enduring and successful peacekeeping missions.

UNDOF's mandate encompasses three essential responsibilities that have guided its operations for nearly five decades. The UN mandated peacekeeping force was tasked with maintaining the ceasefire between Israel and Syria, supervising the disengagement of Israeli and Syrian forces, and overseeing the areas of separation and limitation as outlined in the May 1974 Agreement on Disengagement. This mandate has been consistently renewed every six months since the mission's inception, demonstrating its importance to regional security. Now that the government of Syria has collapsed Israel has taken temporary responsibility of keeping the peace until the new Syrian government can confirm the agreement.

International law may lack the enforcement mechanisms of domestic legal systems, but it shapes state behavior through other means. Understanding it requires looking beyond traditional notions of law to appreciate how shared expectations and reciprocal interests can create order without centralized authority is no small achievement.