Question

In which civilization was the rationalism and secularism of greek thought used to explain religious doctrines? persian empire ottoman empire western christendom abbasid caliphate?

Answer 1

Western Christendom

This was the project of the "scholastics" (or "schoolmen" - what we would call academics) of the Middle Ages.  They explored and analyzed the doctrines of Christianity from a philosophical perspective, drawing not only on philosophical thinking from early church fathers (notably Augustine), but also and especially the thought of Greek philosophers such as Plato and Aristotle.  Thomas Aquinas was enormously influential in bringing an Aristotelian perspective to the theology of the Roman Catholic church.