The Democratic Peace thesis constitutes the most influential use of a classical author – Immanuel Kant – in the contemporary discipline of International Relations. Its central claim that democracies don't fight each other is hailed as coming ‘as close as anything we have to an empirical law in international relations’. Innumerable publications from proponents and critics alike fill the discipline's journals; it has given rise to what one might rightly call a whole industry of quantitative and qualitative studies testing and refining, challenging and refuting its central categories and claims.

Moreover, while academic theories are often hotly debated within their disciplines, they rarely play much of a role outside this narrow circle. This, however, is not true for the Democratic Peace thesis, which has risen to extraordinary influence in the justification of Western or liberal foreign policies in the last decades. But even here its importance does not end. The idea that liberal or democratic states are more peaceful than other states has pervaded the public political discourse in the West to such a degree that it can be presented and reproduced as a self-evident truth in the media.

In the original formulation and argumentation of the Democractic Peace thesis, Kant's ‘Perpetual Peace’ played a crucial role as offering ‘the best guidance’ for an explanation of the statistical evidence of a liberal peace. And even much of the later literature in this field – whether or not it explicitly engages with Kant's argument – routinely cites his name.