Which feature of government does Montesquieu argue for in his book De l'Esprit des Lois (Spirit of Laws) ?

In Spirit of Laws Montesquieu argues for a constitutional government and separation of powers. This entails a government which is based on a paper which has laws written down which have been agreed upon and signed. Separation of powers mean that the Church does not influence the government on decisions and they each rule their institution separately. In Spirit of Laws he also demanded for the abolition of slavery, the preservation of civil liberties and law, as well as the idea that political institutions should reflect the social and geographical aspects of each community.