The author retraces here the historical and founding episode of the First French Republic. It all began with the flight of Louis XVI and the royal family, stopped in Varennes-en-Argonne, on June 21, 1791. The French saw his failed attempt to leave France as blatant collusion with foreigners. Following bitter discussions, during which each party tried to play its card, the National Assembly declared war on Austria and the 1st coalition on April 20, 1792. Disorganized and demoralized, our army suffered severe losses. first several setbacks in the Netherlands before facing and beating, thanks to two exceptional generals, Dumouriez and Kellermann, and the soldiers of the ex-royal army, the best regiments in Europe under the orders of the Duke of Brunswick, their general in chief.