In 1789 the French Revolution commenced, promising practical realization of Enlightenment principles. The Revolution stemmed from the inequalities and inefficiencies of the Old Regime. These included the special privileges of the clergy and aristocracy; an unjust tax system that fell hardest on the rural and urban poor; an outmoded, incompetent, and often corrupt administration and judiciary; a luxurious and vacillating monarchy; and the yearning of the upper bourgeoisie for the privileges of nobility.

Inspired by Enlightenment ideals and the example of the American Revolution, the bourgeoisie and their supporters in the First and Second Estates used the looming financial crisis to force Louis XVI to consider moderate reforms. However, due to a clash of goals and interests, the Third Estate lost much of its clerical and aristocratic support. The procedural controversy in the Estates General prompted the Third Estate to declare itself the National Assembly and, despite challenges by the king and other Estates, began drafting a constitution and advancing reforms. Civil unrest such as the storming of the Bastille, the Great Fear, and the October Days demonstrations, enabled the bourgeois-dominated National Assembly to win acceptance of several crucial reforms: the abolition of clerical and aristocratic privilege; adoption of the Declaration of the Rights of Man and of the Citizen and the Enlightenment principles it articulated; subordination of church to state; the moderate constitution of 1791; reform of the administration and judiciary according to rational principles; and reforms that aided bourgeois business.

In 1792 this moderate stage of the Revolution gave way to a radical stage. The power of the moderates who dominated the National Convention was undermined by foreign invasion, the reactionary Vendée uprising, and dissatisfaction with bourgeois rule among the sans-culottes. These crises enable the radical Girondins to seize control of the Convention. Fear of counterrevolutionary invasion led these radicals to try and execute Louis XVI. Later, another national panic provoked the September Massacres. Supported by the sans-culottes, the more radical Jacobins seized power and introduced far-reaching reforms, including universal manhood suffrage, the abolition of slavery, and economic policies that benefited the poor. The Jacobins also built a centralized administration to meet the crises of the Vendée and royalist invasion. Led by the zealous Robespierre, the Committee of Public Safety marshaled all the resources of the nation, encouraging and channeling extreme nationalism to defeat domestic and foreign enemies. The Terror ended 1794 when Robespierre's enemies, the bourgeois Thermidoreans, arrested and executed him. The Thermidoreans then dismantled the Jacobin government and repealed most of its reforms. During the subsequent Thermidorean reaction many of the Jacobins' reforms were repealed, and a conservative counterterror swept through France. In place of the Jacobin government the Thermidoreans established the Directory, a moderate bourgeois republic that proved incapable of dealing with domestic and foreign crises. In 1799 the Directory fell to Napoleon's military coup.

The French Revolution offered Europe an example of how Enlightenment principles might be realized. That example motivated the efforts of liberal reformers and conservative reactionaries during the nineteenth century. Consequently, liberal democratic ideals continued to advance, displacing old regimes throughout Europe. However, the Revolution also unleashed destructive forces-including extreme nationalism, ideological zeal, and militarism-that culminated with the totalitarian movements of the twentieth century.