I believe separation of religion and state was the accomplishment of Islam. In olden times kings claimed divinity and popes wielded political power. Both these show a inter-mixing of politics and religion. But Islam separated religion and science, put reason on a high pedestal, abolished many superstitions, and promulgated freedom of faith which are all the fundamentals of modern day secularism. But secularism is not to be confused with irreligion as many do today.