Westphalian secularism is neither universal nor 'rational' but Western, the product of a historical process, and it is unintended, cumulative, and incomplete. The recollection of its contingency, specificity and features is an essential prerequisite to overcoming the consistent failure of current international relations, conflict resolution, social integration and related policies, when these are applied to problems with a religious dimension. From the 4 th to the 16 th century Christian theology pervaded all aspects of thought, from the natural sciences to philosophy. When the Reformation destroyed Catholic doctrinal monopoly, much of European thought broke down. 'Secularisation' is the process whereby Europe's Weltanschauung was rebuilt without theology. European conquest spread secular norms across the world, often with stabilising effect. However, when the historical contingency of secularisation is forgotten, and its norms are mistaken for universal ones, conflicts with a religious dimension become irresolvable.

To illustrate secularisation's history and implications, I discuss works by the Leiden Circle around the turn of the 17 th century. The Dutch had to learn to neutralise, and institutionalise the neutralisation of, numerous sources of conflict and instability, including external threats from Spain, France, the Empire and the Papacy, domestic religious, ethnic and social differences, and destabilisingly fast commercial expansion. Arminian politiques like Heinsius, Cunaeus, Grotius and Vossius, realised that conflicting claims that stake their truth-content and validity on religious belief are ultimately irreconcilable. Gradually they removed such claims from acceptable discourse, constructing the comprehensively secularised system of thought that defines modernity. Today's Western conceptual toolkit is very sophisticated, but it cannot perform tasks that its designers deliberately excluded from its cognisance. Mediators in Ireland, the Middle East, the Indian subcontinent or Nigeria routinely assume that conflicts must be solved within a Westphalian framework, through representative democracy and economic interdependence. The policies based on these assumptions are ineffective, often counterproductive. Mistaking Western secular values and methods for universal ones is bad theory, which in turn leads to poor practice. Much of the damage inflicted and institutionally perpetuated by imprudent Western foreign policies and domestic methods of social integration becomes easy to explain, once we recall the historical contingency of secularisation.