Complex sentence: The aristocracy are people considered to be in the highest social class in society, who possess titles granted by a monarch, which once granted them feudal or legal privileges, or deriving, as in Ancient Greece and India, from a military caste.
Split into simpler sentences: The aristocracy are people considered to be in the highest social class in a society which once had a political system of Aristocracy. Aristocrats possess hereditary titles granted by a monarch, which once granted them feudal or legal privileges, or deriving, as in Ancient Greece and India, from a military caste.