States are the prime source of international law within the international legal framework of sovereignty. They not only establish the institutions to apply and interpret the law but also lay down what kind of law shall be applied. States have been doing this since their historical birth without necessarily laying down a text of the law that is to be applied. The law has evolved in their dealings with one another. This has given rise to customary law, the methods of recognizing such law for creating obligations, and then to treaties – to control this evolution more specifically and precisely. Treaties became necessary to cope with complexity, scientific and technological developments and the need for specialized expertise for international relations. The Permanent Court of International Justice (PCIJ) stated in 1927:
International law governs relations between independent States. The rules of law binding upon States therefore emanate from their own will as expressed in conventions [treaties] or by usages generally accepted as expressing principles of law established in order to regulate the relations between these co-existing independent communities or with a view to the achievement of common aims.
As understanding dawned on the governments of States about the indivisibility of mankind and the effects of its conduct, the States have agreed to the emergence of non-derogable norms and non-contractual obligations essential for sheer existence. But sovereignty always keeps its toe in the door of any adjudication on this, through the process of States making reservations as to jurisdiction of forums created by them to decide even on compliance with non- derogable norms or non-contractual obligations recognized by them as intrinsic to the very survival of the human race. Sovereignty also keeps control by reserving to itself the power to put in qualifications to conventions defining such non-derogable and non-contractual norms.
States made reservations to the Genocide Convention’s provision in Article 9, which provided for compulsory jurisdiction of the ICJ for disputes arising under the Convention, and other States objected to these. The ICJ in its Advisory Opinion on Reservations to the Convention on Genocide declared that a State cannot be a party to the Convention by making a reservation which is incompatible with the object and purpose of the Convention. Hence, an objecting State which considers the reservation incompatible can treat the reserving State as not being a party to the Convention; but an objecting State which considers the reservation to be compatible can consider the reserving State to be a party to the Convention. Hence, the State parties are made in charge of treating a reserving party as a party to the Convention or not.
So, State sovereignty, custom and treaty, is the broad framework for understanding the sources of international law.
What is “international”? We use the word “international” when governments of most of the nation states decide to regulate their behavior for cooperation and/or conflict between themselves due to their respective needs and aspirations that necessitate dealing with each other. The internal or national power of each State then meets the internal or national power of other States, despite differences of their internal cultures, social, political and economic orders. This meeting of governments of States, having power to decide about themselves and their people, enables all governments to recognize common natural endowments like high seas, atmosphere, ozone shield, polar regions, water, air and land; common endowments made by human beings, like the Internet; and common threats to both these endowments like poverty, sustainable consumption, lack of health, peace, financial sustainability, free markets and terrorism.