Question: Who wrote a work that described European history until the dawn of the age of the longest serving monarch in European history?
Facts:
Essai sur les mœurs et l'esprit des nations is a work by philosopher Voltaire.
Essai sur les mœurs et l'esprit des nations discusses the history of Europe before Charlemagne until the dawn of the age of Louis XIV, also addressing the colonies and the East.
Louis XIV of France's  reign of 72 years and 110 days is he longest recorded of any monarch of a sovereign country in European history.
Answer: Voltaire