Why was enlightenment philosophy a threat to the European monarchies?

Question

Quizplus · Accepted Answer

Enlightenment philosophy was a threat to the European monarchies because it promoted individual liberty.
Key Takeaway: The Age of Enlightenment was a time in Western philosophy and cultural life in the eighteenth century in which reason was advocated as the primary source and legitimacy for authority. The Enlightenment developed simultaneously in Germany, France, Great Britain, the Netherlands, Italy, Spain, and Portugal. Buoyed by the American colonists' successful rebellion against Great Britain in the American War of Independence, the culmination of the movement spread through much of Europe.
It has been argued that the American Declaration of Independence, the United States Bill of Rights, the French Declaration of the Rights of Man and of the Citizen, and the Polish-Lithuanian Constitution of May 3, 1791, were all motivated by "Enlightenment" principles of rights and individual liberties.

Why Was Enlightenment Philosophy a Threat to the European Monarchies