It would be understandable for a people to say: ‘There shall be no war between us; for we will form ourselves into a sate, appointing for ourselves a supreme legislative executive and juridical power to resolve our conflicts by peaceful means.’ But if this state says: ‘There shall be no war between myself and other states, although I do not recognize any supreme legislative power which could secure my rights and whose rights I should in turn secure’, it is impossible to understand what justification I can have for placing any confidence in my rights, unless I can rely on some substitute for the union of civil society, i.e. on a free federation. If the concept of international right is to retain any meaning at all, reason must necessarily couple it with a federation of this kind.
The concept of international right becomes meaningless if interpreted as a right to go to war. For this would make it a right to determine what is lawful not by a means of universally valid external laws, but by means of one-sided maxims backed up by physical force. It could be taken to mean that it is perfectly just for men who adopt this attitude to destroy one another, and thus to find perpetual peace in the vast grave where all the horrors and violence and those responsible for them would be buried.Kant, Immanuel (1795) Perpetual Peace: A Philosophical Sketch