World peace was not even a pipe dream for much of human history, much less an ascribable ideal. In Western civilization, the ancient Greeks understood peace roughly as agreement between peoples. The Romans, who borrowed much of their culture from the Greeks, had a more general understanding of peace as juridical order. With the rise of Christendom, peace took on a subjective conception, meaning roughly inner peace of the soul. It was not until the Enlightenment that peace came to be understood on a wider scale in which global peace became even conceivable. While French philosophers Charles Irénée Castel de Saint-Pierre and Jean-Jacques Rousseau were the first to propose a project of peace on a wide scale (i.e., beyond one’s immediate bordering countries), Jeremy Bentham and Immanuel Kant provide the most comprehensive theories of world peace in the eighteenth century. Bentham, a utilitarian, argued that we should strive for the greatest happiness for the greatest number of persons, and since war causes the most suffering, we ought to strive toward universal and perpetual peace. Kant, an ethicist who emphasizes the duties humans have to each other, argues that it is our duty to work towards world peace and proposed a League of Nations in order to do so. This chapter chronicles the conceptions of world peace throughout the history of Western civilization from the ancient Greeks to the Enlightenment and show how Kant’s philosophy in particular influenced peace plans of the twentieth century.