"Perpetual Peace: A Philosophical Sketch" (German: Zum ewigen Frieden. Ein philosophischer Entwurf) is a 1795 essay by Immanuel Kant.
In this essay, Kant proposed a peace program to be implemented by governments. The "Preliminary Articles" described these steps that should be taken immediately, or with all deliberate speed:
- "No secret treaty of peace shall be held valid in which there is tacitly reserved matter for a future war"
- "No independent states, large or small, shall come under the dominion of another state by inheritance, exchange, purchase, or donation"
- "Standing armies shall in time be totally abolished"
- "National debts shall not be contracted with a view to the external friction of states"
- "No state shall by force interfere with the constitution or government of another state"
- "No state shall, during war, permit such acts of hostility which would make mutual confidence in the subsequent peace impossible: such are the employment of assassins (percussores), poisoners (venefici), breach of capitulation, and incitement to treason (perduellio) in the opposing state"
Three Definitive Articles would provide not merely a cessation of hostilities, but a foundation on which to build a peace.
- "The civil constitution of all states to be republican"
- "The law of nations shall be founded on a federation of free states"
- "The law of world citizenship shall be limited to conditions of universal hospitality"
Kant's essay in some ways resembles modern democratic peace theory. He speaks of republican, Republikanisch, (not democratic), states, which he defines to have representative governments, in which the legislature is separated from the executive. He does not discuss universal suffrage, which is vital to modern democracy and quite important to some modern theorists; later commentators dispute whether it is implied by his language, although many Enlightenment thinkers advocated a more aristocratic republicanism by men of letters. The essay does not treat republican governments as sufficient by themselves to produce peace: freedom of emigration (hospitality) and a league of nations are necessary to consciously enact his six-point program.
Kant claims that republics will be at peace not only with each other, but are more pacific than other forms of government in general.
The general idea that popular and responsible governments would be more inclined to promote peace and commerce became one current in the stream of European thought and political practice. It was one element of the American policy of George Canning and the foreign policy of Lord Palmerston. It was also represented in the liberal internationalism of Woodrow Wilson, George Creel, and H. G. Wells. Kant's recommendations were clearly represented in the 1940s in the United Nations.
Kant's essay is a three-legged stool (besides the preliminary disarmament). Various projects for perpetual peace have relied on one leg - either claiming that it is sufficient to produce peace, or that it will create the other two.
In the early days of World War I, H.G. Wells stated that it would be "the war to end war", on the grounds that, once Prussian militarism and autocracy was replaced by popular government, European nations would not ever go to war with each other, because militarism and armaments resulted from the German threat. This idea was much repeated and simplified over the next four years; at present, the idea that democracy by itself should prevent or minimize war is represented by various democratic peace theories.
In 1909, Norman Angell relied only upon the second leg, arguing that modern commerce made war necessarily unprofitable, even for the technically victorious country, and therefore the possibility of successful war was The Great Illusion. James Mill had described the British Empire as outdoor relief for the upper classes; Joseph Schumpeter argued that capitalism made modern states inherently peaceful and opposed to conquest and imperialism, which economically favored the old aristocratic elites.
This theory has been well developed in recent years. Mansfield and Pollins, writing in the Journal of Conflict Resolution, summarize a large body of empirical work which, for the most part, supports the thesis . There are various exceptions and qualifications which seem to limit the circumstances under which economic interdependence results in conflict reduction. On the other hand, moving beyond economic interdependence to the issue of economic freedom within states, Erik Gartzke has found empirical evidence that economic freedom (as measured by the Fraser Institute Economic Freedom Index) is about fifty times more effective than democracy in reducing violent conflict. 
The third leg is the old idea that a confederation of peaceable princes could produce a perpetual peace. Kant had distinguished his league from a universal state; Clarence Streit proposed, in Union Now (1938), a union of the democratic states modelled after the Constitution of the United States. He argued that trade and the peaceable ways of democracy would keep this Union perpetual, and counted on the combined power of the Union to deter the Axis from war.
Jeremy Bentham proposed that disarmament, arbitration, and the renunciation of colonies would produce perpetual peace, thus relying merely on Kant's preliminary articles and on none of the three main points; contrary to the modern theorists, he relied on public opinion, even against the absolute monarchy in Sweden. Many have followed him since.