Here is the link to a rather good article I read recently that discusses the separation of church and state. It includes the idea that the nation-state, an area with long standing geographical boundaries, is a relatively new invention in the last 400-500 years after the relative fluidity of the empire nations. I enjoyed Fr. Stephen Freeman's brief explanation of how and why the Christian church gets itself in trouble when it tries to make the same delineation between itself and a secular ruling government.
Then seek out the article titled:
Church & State Are Not Separate--They Are At War
by Fr. Stephen Freeman
Orthodox Church of America
Rector of St. Anne Orthodox
Oak Ridge Tennessee