After France declared war on Austria on 20 April 1792 and following early encounters in which French arms did not distinguish themselves, anti-revolutionary forces advanced into France (18 August 1792).The combined invading force comprised Prussians, Austrians, Hessians and émigrés under the Duke of Brunswick, representing the supreme command of King Frederick William II of Prussia. The commanders-in-chief of the French armies that had formed became one after another "suspects"; and before a serious action had been fought, the three armies of Rochambeau, Lafayette and Luckner had resolved themselves into two commanded by Dumouriez and Kellermann.
The invading allies readily captured Longwy and slowly marched on to Verdun, which was more indefensible even than Longwy. The commandant, Colonel Beaurepaire, shot himself in despair, and the place surrendered on 3 September 1792. Brunswick now began his march on Paris and approached the defiles of the Argonne. But Dumouriez, who had been training his raw troops at Valenciennes in constant small engagements, with the purpose of invading Belgium, now threw himself into the Argonne by a rapid and daring flank march, almost under the eyes of the Prussian advanced guard, and barred the Paris road, summoning Kellermann to his assistance from Metz. Kellermann moved but slowly, and before he arrived the northern part of the line of defence had been forced. Dumouriez, undaunted, changed front so as to face north, with his right wing on the Argonne and his left stretching towards Châlons, and in this position Kellermann joined him at Sainte-Menehould on 19 September 1792.
Brunswick meanwhile had passed the northern defiles and had then swung round to cut off Dumouriez from Châllons. At the moment when the Prussian manceuvre was nearly completed, Kellermann, commanding in Dumouriez’s momentary absence, advanced his left wing and took up a position between Sainte-Menehould and Valmy. The result was the world-renowned Cannonade of Valmy (20 September 1792). Kellermann’s infantry, nearly all regulars, stood steady. The French artillery justified its reputation as the best in Europe, and eventually, with no more than a half-hearted infantry attack, Brunswick broke off the action and retired.
This trivial engagement was the turning-point of the campaign and a turning point in the world’s history. Ten days later, without firing another shot, the invading army began its retreat. Dumouriez’s pursuit was not seriously pressed; he occupied himself chiefly with a series of subtle and curious negotiations which, with the general advance of the French troops, brought about the complete withdrawal of the allied invaders from the soil of France.