States are sovereign entities vis-A-vis each other in the international arena. There are several basic sources from which rules regulating their conduct toward each other emanate, to wit: treaties, customs and certain general principles. The lack of a vertical centralized authority to formulate rules governing the conduct of nations is the most salient feature of today's international law, yet such an authority is assumed to be an essential part of any mature legal system rather than a luxury. However, treaties serve the purpose of the next best method of legislation in the international system: they are rules expressly agreed upon by the signatories thereto. Conventions, i.e. treaties open to universal subscription, are notably quasi-legislative in character due to their almost universal application.
Charles R. Passafiume,
The Living Treaty Power,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol6/iss4/5