International Law is the body of rules considered legally binding in the relations between national states, also known as the law of nations. It is sometimes called public international law in contrast to private international law (or conflict of laws), which regulates private legal affairs affected by more than one jurisdiction.

International law includes both the customary rules and usages to which states have given express or tacit assent and the provisions of ratified treaties and conventions. International law is directly and strongly influenced, although not made, by the writings of jurists and publicists, by instructions to diplomatic agents, by important conventions even when they are not ratified, and by arbitral awards. The decisions of the International Court of Justice and of certain national courts, such as prize courts, are considered by some theorists to be a part of international law. In many modern states, international law is by custom or statute regarded as part of national (or, as it is usually called, municipal) law. In addition, municipal courts will, if possible, interpret municipal law so as to give effect to international law.

Because there is no sovereign supernational body to enforce international law, some older theorists, including Thomas Hobbes, Samuel Pufendorf, and John Austin have denied that it is true law. Nevertheless, international law is recognized as law in practice, and the sanctions for failing to comply, although often less direct, are similar to those of municipal law; they include the force of public opinion, self-help, intervention by third-party states, the sanctions of international organizations such as the United Nations, and, in the last resort, war.

National states are fundamentally the entities with which international law is concerned, although in certain cases municipal law may impose international duties upon private persons, e.g, the obligation to desist from piracy. New rights and duties have been imposed on individuals within the framework of international law by the decisions in the war crimes trials, by the genocide convention, and by the Declaration of Human Rights.

Throughout History people have tried to create organizations which could institute some kind of International Law. Every since the first to nations traded with each other their were always rules and customs regarding the way the two nations were to behave toward each other. As man developed organizations began to regulate the behavior of nations. During the Middle Ages the Catholic church had the power to crown kings and declare holy wars such as the crusades. During the 1500s-1700s nations were regulated in Europe by system of maintaining what was known as the balance of power. During the 1800s and the early twentieth century the Bismarck system of alliances maintained International order. However, the alliance system eventually lead to the first World War.

World War 1 Alliances.

The close of the first World War lead to the creation of the first body designed to handle International Law and to prevent future wars from happening. This body was the League of Nations. It was proposed by President Woodrow Wilson of the United States at the end of the first World War as part of his 14 points for peace. 

http://www.unog.ch

It is an interesting irony that the United States, whose President proposed the organization, did not actually join the United Nations. This was one of the major stumbling blocks the League had to deal with from its founding. Another important nation that didn't join was Germany, this too would come back to haunt the League. 

From the beginning the League had little power to solve the problems it intended to solve. The only collective power that was agreed upon was the power to impose economic sanctions. Without the ability to use military force in extreme circumstances or even to send peace keepers, it had no way of enforcing its will. 

However, the League can claim some accomplishments. The Geneva Conventions were adopted as a source of international Law, and these would later be endorsed by the UN. Also, the World Court was created in the Hague, and it would serve as the basis for the Nuremberg trials and the ICJ.

Peace Palace, Hague

The outbreak of World War 2 signaled the end of the League. It failed in its primary mission to prevent another global war. However, out of the ashes of World War 2 came the modern body of International Law, the United Nations, which had managed to last to today. The advent of revolutionary technology and growing globalization of companies and business has lead to the strengthening of the UN as a source of International Law, in a world that is getting smaller every day. 

signing the UN Charter.

MORE INTERNATIONAL LAW RESOURCES:

MegaLaw.com International Law links
FindLaw.com International Resources
European Journal of International Law