Public international law is the body of law concerned with the interaction of sovereign states, as well as entities such as multinational corporations and non-governmental bodies. Simply put, public international law governs the way states interact with one another, while national law governs how citizens behave within states and private international law governs the ways in which citizens from different states interact. International laws regulate trade, shipping, air travel, communications, the conduct of war, human rights, and other topics. This type of law is a complex and often-disputed field.
The origin of modern public international law is usually dated to the Peace of Westphalia in 1648. This diplomatic congress ended the Thirty Years' War, establishing the modern idea of the sovereign nation-state. The writings of legal thinkers such as Hugo Grotius (1583-1645) influenced the origins of international law during this period. Grotius argued that nations should be governed by moral principles, and that the community of states ought to be regulated by treaties and agreements between nations.
A model of public international law based on treaties between sovereign nation-states dominated international relations well into the 19th century. Treaties between nations were seen as the safest way of guaranteeing peace. As the European powers clashed over territory and authority, however, many became concerned that the international system of treaties was threatening peace between nations rather than upholding it. This concern came to a head following World War I. Many observers believed the intricate network of alliances in Europe had been a major cause of the war.
After the war, the victorious nations attempted to create a multilateral framework for ensuring peace. The League of Nations was unable to enforce adherence to international law, though, and states such as Italy and Japan defied the organization's rules with impunity. Following World War II (WWII), the United Nations (UN) was formed to maintain peace and implement new conventions regulating international behavior. The work of the UN and other intergovernmental organizations resulted in the post-WWII period seeing a greater degree of success in international law enforcement, although many contentious issues remain into the 21st century.
Contested areas in public international law include human rights and the conduct of war, as well as economic issues such as fishing rights. Even in the case of an established international consensus, there are a number of obstacles to enforcing international law. The most significant problem is national sovereignty: Every state is the final authority over its own conduct, so it is difficult to enforce international standards on nations that do not voluntarily agree to them. Enforcement mechanisms can include diplomatic pressure, economic sanctions, and even military intervention. Crimes against international law are judged by the International Court of Justice, the judicial arm of the UN.
Despite the problems of enforcement, public international law plays a vital role in the functioning of the world community. By providing a basis for cooperation between governments, international agreements and conventions permit governments to deal with problems beyond their individual ability. States or groups that go against the conventions of international law harm their reputations and face potentially serious consequences.