On September 20, 1792, French forces earn their first major victory against the Prussians during the War of the First Coalition. In France, the French Revolution was in full swing with the power of King Louis XVI weakened and the Legislative Assembly holding representing the citizens of France. Concerned over the threat to the monarchy and stability in Europe, neighboring kingdoms and empires made statements and threats in support of the French monarchs, including the Declaration of Pilnitz made by King Frederick William II of Prussia and Holy Roman Emperor Leopold II. In reaction to the threats and actions taken by its neighbors, the revolutionary French government declared war on Austria.

Soon thereafter, veteran Prussian forces invaded France and repeatedly defeated the French military (consisting of many inexperienced volunteers). The tide of war changed on at Valmy on September 20 as two French armies commanded by General Charles Demouriez and General François Kellerman took up positions halt the Prussian advance on Paris. The French forces consisted of many new, enthusiastic volunteers with a professional, skilled, and well-trained force of troops of the old Royal Army at its core, including some of the best artillery in Europe. A duel between the opposing artillery forces ended in a French victory. Following a failed attempt to advance under heavy fire and growing enthusiasm among the French defenders, the Prussian forces withdrew. While there is still debate as to why the Prussian commander, the Duke of Brunswick, ordered a retreat, the most likely explanation was that he was reluctant to suffer the high casualties which would be incurred by pressing the attack at a time the issue of Prussia's defenses to the east were in question (Russia had invaded neighboring Poland just a few short months earlier).

The fortunes of the Prussian campaign now reversed as the French chased them back out of France, taking the German city of Mainz in October. On the day of the Battle of Valmy, the Legislative Assembly transferred power to the National Convention. The new of the great victory emboldened the revolutionaries of the assembly, who then abolished the monarchy in France and established the First French Republic over the following couple of days.