For centuries philosophers and reformers promoted the vision of a more lawful international order as an essential requirement for peace. Just as the development of law helped to create order and reduce violence within domestic societies, it was hoped that the emergence of international law would tame the anarchy of political relations among nations. The early peace societies in the United States and Europe were internationalist in outlook and experience, and many actively campaigned to establish agreements and institutions for the arbitration of international disputes. During the nineteenth century the first practical steps were taken to establish and codify principles of international law, as part of a movement to regulate and humanize the conduct of war and to establish mechanisms for preventing the outbreak of war. The decades that followed saw the creation of international law societies, agreements to regulate transnational commerce and communications, the beginnings of international arbitration, and the emergence of a wide array of legal agreements to regulate and prevent conflict among nations. Thus began a movement that has continued to this day toward ever expanding networks of international law and multilateral institutions.

Analyzing the movement for internationalism poses conceptual challenges, and reveals complex and sometimes contradictory impulses among those involved. The terminology available – internationalism, pacifism, peace advocacy – is too imprecise to capture the many differences in nuance and political perspective that exist. As described below, internationalism can be either conservative or liberal.