The primary impact of the Enlightenment on European monarchies was the challenge it posed to their absolute authority. Enlightenment thinkers promoted ideas of liberty, reason, and individual rights, which led to questioning the divine right of kings and advocating for more democratic forms of governance. Philosophers like Locke and Rousseau argued for the social contract and the idea that governments should reflect the will of the people rather than the whims of monarchs. These concepts influenced revolutions, such as the American and French Revolutions, encouraging citizens to demand constitutional reforms or even overthrow tyrannical regimes, ultimately leading to the decline of absolute monarchies in Europe.