I can quote from historial resources if you are truly intersted. Many historians point out that it only under Muslims kings that we can find people of different faith coexisting. Because in those days the subjects of the king has to automatically embrace the faith of the Kind. You cant give a good example of an empire where the subjects and the king had two different religion. As an example - see how Muslims ruled the spain for 800 years,when christians conquered they simply massacred the whole of Muslim population.
Read this Two Time Pulitzer Prize winning author-s ground breaking New Book God's Crucible-Islam and the Making of Europe-This book explains how Muslim spain's legacy of tolerance and rich heritage of scientific accomplishments shaped Europe.
This is one of Washington Post's publication's review of the book
