International relations, study of the relations among states and other political and economic units in the international system. Particular areas of study within the field of international relations include diplomacy and diplomatic history, international law, body of rules considered legally binding in the relations between national states, also known as the law of nations. It is sometimes called public international law in contrast to private international law (or conflict of laws), which regulates private legal. Click the link for more information., international organizations, international finance and economics, and communications, among others. In addition, increased attention has been paid in recent years to developing a more scientific understanding of the international system as a whole. Aspects of international relations have been studied as early as the time of the ancient Greek historian Thucydides.