Synopsis International relations, study of the relations among states and other political and economic units in the international system. The history of international relations is often traced back to the Peace of Westphalia of 1648, where the modern state system was developed. Prior to this, the European medieval organization of political authority was based on a vaguely hierarchical religious order.

International relations represent the study of foreign affairs and global issues among states within the international system. International society is a moving complex of overlapping and nested structures and situations of conflict, power balancing, balances of powers, and structures of expectations.