What is international law primarily based on?

International law is primarily based on international customs. This foundation arises from the practices and norms that have developed over time through the interactions of states and other international actors. These customs become accepted as binding, helping to establish the principles that govern the relationships between countries.

International customs can be seen in the form of unwritten laws that evolve from the consistent practices of nations, accompanied by a sense of legal obligation, which is referred to as "opinio juris." Recognizing these customs helps to facilitate international cooperation and establish expectations for behavior among states, which is vital for maintaining order and peace in the international arena.

National constitutions, state statutes, and local ordinances are confined to individual countries or jurisdictions and do not have the transnational applicability or recognition that international customs do. Therefore, they do not serve as the primary basis for international law.