Because the ancient and classical worlds lacked an understanding of the state (or any other form of polity) as a sui generis entity in possession of rights and subject to obligations, a fully developed system comprehensively regulating the behavior of polities was neither possible nor conceivable for them. There were a great number of treaties in the ancient world which addressed a wide range of political and economic issues, but they differed from modern international legal instruments in two important respects: they were viewed as personal pledges by one ruler to another, that perforce did not survive those rulers, and there were no system-wide rules regulating treaties themselves other than the (unarticulated) principle pacta sunt servanda insisting that agreements are binding upon the parties.
