At the opening of the year, Dumouriez chose to ignore orders from the government in Paris to defend Belgium and instead began an invasion of the Netherlands, hoping to overthrow the stadtholder and establish a popular republic backed by France. In the event, he took Breda in Brabant and prepared to cross into Holland and capture Dordrecht. However, the armies remaining in Belgium suffered a number of defeats, with the Austrians winning battles at Aix-la-Chapelle and Liège and raising Miranda's siege of Maastricht. Dumouriez was forced by his superiors to return to Belgium and take command.
After a defeat at Neerwinden, Dumouriez had to retreat from Belgium. He then made an agreement with the Austrians to hand over to them several border fortresses in return for a truce where he could march on Paris and restore the monarchy under the Constitution of 1791. However, he was unable to secure the loyalty of his troops, and he defected to the Austrian lines rather than face arrest by the Jacobins.
At the same time, the increasing power of radicals in Paris incited revolt in the provinces, with the people of Lyon and Marseille rebelling and the Vendée raising an army to attack the central government and open communications with Britain. Spanish armies crossed the Pyrenees, Sardinian armies the Alps, and Austrian armies occupied Valenciennes and forced the northern armies back on Paris. Britain ordered a naval blockade of France on May 31.
The revolutionary government prepared a full mobilization of the nation (see Levée en masse), showing no mercy to internal or external enemies. According to Mignet's History of the French Revolution, "The republic had very soon fourteen armies, and twelve hundred thousand soldiers. France, while it became a camp and a workshop for the republicans, became at the same time a prison for those who did not accept the republic." They proceeded to suppress Caen, Lyon, and Marseille, although the counter-revolutionary forces turned Toulon over to Britain and Spain on August 29, resulting in the capture of much of the French navy, and Toulon was not retaken by Dugommier (with the assistance of the young Napoleon Bonaparte) until December 19.
In September, Houchard defeated the Duke of York at Hondschoote, forcing him to abandon the siege of Dunkirk. In October Jean-Baptiste Jourdan, taking over the northern armies, won the Battle of Wattignies and returned to the offensive, but did not make major gains before the winter.
In the Pyrenees, the French armies ended the year on a defensive posture near the border, while on the Alpine frontier, a French invasion of Piedmont failed.