"The Function of Knighthood"

Sometime in the 1100's John of Salisbury wrote a treatise entitled Policraticus.  Here is an excerpt, from J. Dickinson's translation, included in the anthology The Portable Medieval Reader:

For soldiers...are the more loyal to their prince in proportion as they more zealously keep the faith of God...

A cynical view of culture is that it exists to justify the position of the powerful.  At different times in history even the religious principles of the socially disruptive Christian faith have been turned to that end.