The freedom of monarchs to tyrannize was most impacted.
The Age of Enlightenment (Europe, XVIII Century) was marked by the valorization of human intelectual faculties above all. It was an intellectual movement that sustained the use of reason (Light) against the old regime (Darkness). As such, one of the main critics against the old regime was towards the monarchy absolutism. With the quick dissemination of the Enlightment ideals throughout the population, some absolutist kings began to accept some of these ideals, in order to avoid losing their governance or, worse, their heads. These kings were called enlightened despots.
Under the idealist slogan 'Egalité, Liberté et Fraternité', it promoted several changes in Politics, Economy and Society in general.