The Council in Paris was bewildered by the speed with which Gaspard Lefebvre raised a volunteer army of 45,000 men to save southern France, but facing an existential threat from the Austro-Russian invasion, they allowed the insubordinate general to proceed. Integrating veterans from his previous campaigns with new recruits, Gaspard marched south in May 1803 with his trusted generals—Dubois, Davout, d’Ornano, and Massena. Upon reaching the vicinity of Lyon, he devised a strategy based on intelligence suggesting the Austrian commander, General von Thalheim, would remain defensive within the city. Gaspard planned to isolate and destroy the smaller Russian army under General Babayev near Tarare, while General Dubois’ cavalry division was sent away to harass Austrian supply lines and ensure they remained pinned in Lyon.

On June 1st, the plan appeared to succeed as French forces engaged the Russian army at the Battle of Tarare. After a day of intense artillery duels and infantry clashes, General d’Ornano’s light cavalry executed a flanking maneuver that shattered the Russian rear. The Russian lines collapsed into a chaotic rout, granting the French a decisive victory. However, the situation changed drastically the following morning when the Austrian army, defying French intelligence, arrived on the field to launch a surprise attack. With Dubois’ heavy cavalry absent and the French troops exhausted, the Austrian artillery and infantry assaults began to decimate Gaspard's lines, threatening to annihilate the French army.

Gaspard and Dubois rushed back to the battlefield, but their initial cavalry charge failed to break the disciplined Austrian squares. With the French army on the brink of destruction, the infantry launched desperate, near-suicidal bayonet charges to hold the line. The momentum shifted only when a serendipitous artillery strike caused a massive explosion in an Austrian ammunition wagon, stunning their regiments. Seizing the confusion, the French cavalry and infantry launched a final, ferocious assault that broke the Austrian resolve, turning a near-defeat into a total rout and forcing the coalition forces to retreat out of France entirely.

Following the victory, the Austro-Russian forces were chased into neutral Switzerland, effectively ending the threat to the Republic. Russia, disillusioned by the defeat and a lack of British funding, signed a separate truce in July. Left isolated, Austria was forced to the negotiating table. In October 1803, Gaspard signed the Peace of Milan, which secured French annexation of the Austrian Netherlands and the Rhineland, recognized the annexation of Savoy, elevated Bavaria to a kingdom, and reorganized Northern Italy into a French-aligned republic. With a subsequent ceasefire signed with Britain in early 1804, the continent finally entered a period of peace, with France established as the dominant power in Europe.