The Spirit of the Laws
Montesquieu spent around twenty one years researching and writing De l'esprit des lois, covering many topics including law, social life and the study of anthropology, and providing more than 3,000 commendations. In this treatise Montesquieu argued that political institutions needed, for their success, to reflect the social and geographical aspects of the particular community.  He pleaded for a constitutional system of government with separation of powers, the preservation of legality and civil liberties, and the end of slavery.