Secularism has long been regarded as a settled, non-controversial feature of Western societies. While a century or more of intra-Christian wars more or less gave way to the principle agreed in the Treaty of Westphalia of 1648, Cujus regio, ejus religio (‘The religion of the prince is the religion of the people’), namely that the religion of the ruler was to be the religion of the state/country, 1 this principle was subsequently chipped away at. Not only did toleration come to be seen as equally important but the Enlightenment of the eighteenth century in various ways challenged the Christian faith, the authority of the Church, and the promotion of a religion by the state. With the militant example of the French Revolution, the secularist anti-Westphalian principle of the separation of Church and state, of religion and politics, has progressively become hegemonic. By the middle of the twentieth century it was universally taken for granted in Western societies – one of the few principles that was shared by liberalism, socialism and most versions of nationalism – and thought to be one of the defining features of modernity. Moreover, the Westphalian prioritizing of territorial allegiance over doctrinal truth and allegiance to a community of co-believers has been triumphant in the politics of Western societies. It has not been entirely without its challengers but the challengers have been forms of secular internationalism such as socialism or cosmopolitanism, rather than religious communities or movements.