What led to the revival of natural law?

Towards the end of the nineteenth century, a revival of the ‘natural law’ theories took place. The two main reasons which led to the revival of natural law are: First, a reaction against nineteenth century legal theories which has exaggerated the importance of ‘positive law’ was due; Second, it was realized that abstract thinking or a priori assumptions were not completely futile. The pure positivist failed to solve the problems created by the changed social conditions.