Campaigns of 1792 in the French Revolutionary Wars The French Revolutionary Wars began in 1792 . Preparations . France declared war on Austria on 20 April 1792 . But Prussia and other powers had allied themselves with Austria in the expectation of conflict , and thus France faced a coalition and not a single power at the moment when the " emigration " , the ferment of the Revolution , and want of material and of funds had thoroughly disorganised her army . The army behaved badly in the first engagements . Near Lille ( 29 April ) the French soldiers fled at sight of the Austrian outposts and murdered their general Théobald Dillon , whom they accused of betraying them . The commanders - in - chief of the armies became political " suspects " ; and before a serious action had been fought , the three armies commanded respectively by Rochambeau , Lafayette and Luckner had been reorganized into two commanded by Dumouriez and Kellermann . Thus the disciplined soldiers of the Allies had apparently good reason to consider the campaign would be easy . On the Rhine , a combined army of Prussians , Austrians , Hessians and émigrés under the Duke of Brunswick was formed for the invasion of France , flanked by two smaller armies on its right and left , all three being under the supreme command of King Frederick William II of Prussia . In the Southern Netherlands , plans called for the Austrians to besiege Lille , and in the south the Piedmontese also took the field . The first step was the issue ( 25 July ) of the Brunswick Manifesto , a proclamation which , couched in terms in the last degree offensive to the French nation , generated the spirit that was afterwards to find expression in the " armed nation " of 1793 – 1794 , and sealed the fate of King Louis . It was issued against the advice of Brunswick himself , whose signature appeared on it ; the duke , a model sovereign in his own principality , sympathised with the constitutional side of the French Revolution , while as a soldier he had no confidence in the success of the enterprise . Invasion . After completing its preparations in the leisurely manner of the previous generation , his army crossed the French frontier on 19 August 1792 . The Allies readily captured Longwy and slowly marched on to Verdun , which appeared more indefensible even than Longwy . The commandant there , 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 advance 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 Châlons . At the moment when the Prussian manoeuvre 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 , the duke broke off the action and retired . This seemingly minor engagement proved the turning point of the campaign and a watershed in world history . Ten days later , without firing another shot , the invading army began its retreat . Dumouriez did not press the pursuit seriously ; 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 enemy from the soil of France . Other fronts . Meanwhile , the French forces in the south had driven back the Piedmontese and had conquered Savoy and Nice . Another French success was the daring expedition into Germany made by Custine from Alsace . Custine captured Mainz on 21 October 1792 and penetrated as far as Frankfurt . In the north , the Austrian siege of Lille had completely failed , and Dumouriez now resumed his interrupted scheme for the invasion of the Netherlands . Controlling enormously superior forces , he made his advance late in the season and surprised the Austrians . On 6 November he won the first great victory of the war at Jemappes near Mons and , this time advancing boldly , he overran the whole country from Namur to Antwerp within a month . Cultural representations . " Original text from 1911 Encyclopædia Britannica "