The French Revolution
The 1789 uprising that overthrew the Bourbon monarchy, beheaded the king, and gave the modern world the political vocabulary of left/right, citizen, and revolution itself.
Origin
On July 14, 1789, a Paris crowd stormed the Bastille fortress-prison. Within months the National Assembly had abolished feudalism and adopted the Declaration of the Rights of Man and of the Citizen. Louis XVI was executed by guillotine in January 1793; the radical Jacobins under Robespierre presided over the Terror; Robespierre himself went to the guillotine in July 1794. Napoleon eventually rose from the chaos and turned the republic into an empire. The revolution exported its slogans (liberté, égalité, fraternité), its calendar, its metric system, and its assumption that legitimate governments rest on the consent of the governed.
Modern usage
The reference point for every later revolutionary moment — invoked in 1830, 1848, 1917, 1968, the Arab Spring, etc. 'Storming the Bastille,' 'Reign of Terror,' 'let them eat cake' (probably never said by Marie Antoinette) are all in ordinary English. The left/right terminology in politics comes from the seating arrangement of the 1789 National Assembly.
Tags