Belgium did not exist like today, it was an integral part of the Austrian Netherlands, the same Netherlands were divided into two camps, one side of the Dutch Protestant (current Netherlands) and the other Belgian Catholics (the southern Netherlands). The Principality of Liège was independent.

In Champagne, the generals Dumouriez and Kellermann, newly appointed, arm in haste volunteers. Their army of professional soldiers and volunteers gather on the plateau of Valmy.
47,000 French backed a mill are soon faced with 34,000 Prussians under the command of the Duke of Brunswick. When the fog dissipates, Kellerman raises his sword, surmounted by a plume in the hat
light, and shouted: Vive la Nation. The soldiers imitate and sing La Marseillaise.
One Gun Salute to unimportant place. The Prussian infantry up to the assault, but fell almost immediately under the fire of 36 guns. For the first time since the war began, the French attack encaissent
without hesitation.
The Duke of Brunswick was taken aback by this resistance. 20,000 balls in total are exchanged before deciding to withdraw. The Gun Salute was altogether less than 500 victims (300 in
French, the Prussians at 184). The Prussians, soaked by rain and made sick by dysentery they caught in the vineyards of Champagne, wisely beat a retreat.
The French not to continue, which will be worth later the generals on both sides to be suspected of treason.
Meanwhile, France is preserved from the invasion. The Revolution can continue.

With a first success in Valmy, the young French Republic decided to push his advantage against the Prussians and the Austrians who threaten invasion.
In Belgium, possession of the Hapsburgs from Charles V, they wear their effort.
The Austrian army of the Duke of Saxony-Teschen, who takes his winter quarters, was taken by surprise by the attack of Charles François Dumouriez, winner of Valmy.
The Battle of Jemappes is part of the campaign by the armies of the young French Republic to export revolutionary model. The Northern army was commanded by Dumouriez which by various maneuvers diversions, had succeeded in fixing the Austrian troops on a front stretching from Flanders to the Ardennes. For comparison of Jemappes, he was able to gather forces two to three times
larger than the Austrians.
Collected in Valenciennes, troops Dumouriez (below) took off from the mill Boussu 3 and 4 November 1792.

The next day the French and Austrian armies were facing. Have not benefited from the weakness of the left side, Dumouriez general forecast an attack on 6 November during which he initially thought it could encircle the Austrians and end with action at center.

The Battle of Jemappes (Jemmapes at the time) committed on 6 November 1792 to 7 in the morning to the sound of the Marseillaise. After an artillery duel ineffective from 7am to 10am, Dumouriez attack front but the french are
stopped by fire redoubts. D'Harville with volunteers who have never suffered fire dare not move and remains inactive. Right Beurnonville can not move forward, blocked by a very strong resistance.
On the left, Ferrand Caussade climbed to the heights of Jemappes with six battalions and falls on the right side of the Austrian drives. Immediately, it is noon, the center line between french but faces new
Fire terrible Austrian batteries. Approaching the enemy lines the shooting of the hunters Tyrol and the threat of the Austrian cavalry arrest and then reduced. After a moment of hesitation,
the Duke of Chartres supports these brigades and revival against the Austrian center and folds back on Mons. Beurnonville still blocked on the right Dumouriez door leads to the battalions in the song of the Marseillaise,
  "In your turn, my children!" they would have screamed. All the Austrian craque now and ebbs in Mons. The victory is won.
The Austrian retreat in the direction of Mons. If the General Harville had executed the orders of the Austrian army Dumouriez could only capitulate.
Forces involved -> France: 40 000 men, Austria: 26 000 men.
Losses -> France: 1 950 dead, Austria: 1 241 dead.

Jemappes is not a strategic battle tactics or even, it is a battle front, the most costly in human life. The battle is confusing, the victory is achieved is difficult and dearly paid
but its impact in Europe is enormous. It recognizes new and the French armies of the Republic's ability to win battles. Jemappes livrait Belgium at the French armies, the Austrian who preferred evacuate without thought of defending it. Dumouriez entered Mons on November 11, November 15 in Brussels and November 28 in Liege. His lieutenants at the same time interval took Charleroi, Namur (2/12/1792), Ostend, Bruges, Ghent and Antwerp (30/11/1792). Beginning in December 1792, is the conquered Belgium, Aachen is occupied and Belgium said severed its ties with Austria and wanted to be in the Republic.
From 1793, Hainaut is attached to France and took the name "Department of Jemappes. The first french connection is short. Indeed, on 18 March 1793, the French were beaten at Neerwiden. For the third
  times, Austria gets the Netherlands and restore the Old Regime. But the battle of Fleurus (June 26, 1794) inaugurates the return of French.

On 1 October 1795, a decree of the Convention of all the Belgian territories, divided into nine departments, France. The Department of Jemmapes acquires a configuration that is always that of the province of Hainaut.
The period that saw the French territories that now make up Belgium is a pivotal time in the history of this country: it establishes, in effect, the end of privileges and the seigneurial system, the birth of human rights, of a new institutional, economic, social and legal. It places on the front of the stage a character previously deleted in the political debate: the people. It leaves deep traces not only in the legislative or administrative organization, but also in the most mundane gestures of daily life: think of upheaval caused by the generalization of the metric system
or paper money. Finally, for our country, then seals the meeting French provinces of the southern Netherlands with the Principality of Liege.