In 1880, the German intellectual historian Otto von Gierke published a book entitled Johannes Althusius und die Entwicklung der naturrechtlichen Staatstheorien. Those few who were familiar with the main protagonist of Gierke's volume would have wondered at his choice of subject, for Althusius's thought was outdated almost as soon as it was published. The societal and political theories of the German jurist were based largely on soon-to-be-outdated modes of analysis and understanding. Only a decade after his death, the Treaty of Westphalia ended the so-called Thirty Years War, and a series of new national and international orders were gradually ushered in. Althusius's death in 1638 was a kind of harbinger of the death of the pre-modern European political order. Both his ideas and the medieval structures of European society which he was reflecting on seemingly became obsolete. Given all of these facts, Gierke's attempt to resurrect Althusius seems all the more puzzling.

Rather than attempting a rehabilitation of Althusius by arguing for his significance as a political thinker (as per Gierke) or dismissing him as largely irrelevant (as per most others), this chapter aims to demonstrate Althusius's role in the desacralisation of the confessional state in Europe and the broader secularisation of political thought. The role of Althusius in this story is mixed. He displays continuity with earlier Reformed thinkers in his theory of natural law and his understanding of the origins of political life. This is, in part, because Althusius's ideas were deeply imbued with Aristotelianism. These aspects of his thought, his Aristotelianism and his natural law theory, will occupy the initial sections of this chapter. First, we will examine his conception of natural law. As we will see, this aspect of Althusius's thought is reminiscent of Thomas, as well as Calvin and Hooker. He retained a strong connection between God and the purpose and operations of the natural law. Second, we shall address Althusius's theory of the origins of political society, a theory which was clearly Aristotelian and naturalist. I will argue that these two key elements mean that Althusius retained a sacred foundation for political life.

However, in the third instance, we will see that Althusius played a part in introducing an idea into the Reformed Protestant political theory vocabulary which would influence the tradition in a secular direction. This idea is that of pactum.