The three sieges of Charleroi between 30 May and 25 June 1794 were at the heart of the French offensive on the Sambre in the summer of 1794, and the defeat of an Allied relief army at Fleurus on 26 June was the decisive moment of the entire two year long campaign in the Austrian Netherlands. At the start of 1794 the French decided to take advantage of their massive advantage in numbers to launch offensives at both ends of the Allied front line. While General Pichegru, with most of the Armée-du-Nord, won a series of successes in Flanders, ending with the defeat of an elaborate Allied attack at Tourcoing (17-18 May), the campaign on the Sambre was rather less successful.
At the start of the campaign the French suffered from a divided command. The army on the Sambre was made up of part of the Army of the Ardennes under General Louis Charbonnier and the right wing of the Armée du Nord under General Jacques Desjardins. The two generals were under constant pressure from the representatives of the Committee of Public Safety, and were well aware that their lives were on the line. At the start of the campaign in May 1794 50,000 French troops were facing 30,000 Austrian and Dutch troops under the command of Prince Wenzel Anton Graf Kaunitz.
Over the course of the campaign the French crossed the Sambre five times, and besieged Charleroi three times. Each time the Allies responded in force, and on the first four occasions successfully forced the French to retreat. The first crossing came on 12 May, and was the least successful of the five, for the French were forced to retreat on the following day. The second crossing was made on 20 May. Once again the Austrians attacked on the next day. This attack failed, but a second attack on 24 May once again forced the French to retreat.
The third crossing of the Sambre came on 26 May, and caught the Allies in the middle of a reorganisation of their forces. While the Prince of Orange took over from Kaunitz, the French advanced towards Charleroi, and from 30 May-3 June besieged the city. The Allies counterattacked on 3 June, ending the first siege, and forcing the French back across the river.
On 4 June General Jourdan reached the front with part of the Army of the Moselle, giving the French a much bigger numerical advantage. Eventually the composite army would be renamed as the Army of the Sambre and the Meuse, but even before that the combined army came under Jourdan's command. On 12 June he led the French across the Sambre for the fourth time, and besieged Charleroi for the second time. This siege was no longer than the first, for on 16 June the Allies counterattacked again, and Jourdan was forced back across the Sambre. This time the Allies believed that the French were too badly demoralised to make a fifth crossing, and the prince of Saxe-Coburg moved some of the Prince of Orange's west to deal with the threat from Pichegru.
This was a mistake, for on 18 June Jourdan led his army across the Sambre for a fifth time, and the French besieged Charleroi for the third time. This time the Allies were not strong enough to respond with an immediate counterattack, and Saxe-Coburg was forced to move east to take command in person. On 25 June the revolutionary leader and key figure in the terror, Louis Antoine Léon St. Just, summoned Charleroi to surrender, and despite the third siege only being one week old, the tiny garrison surrendered.
On the following day Saxe-Coburg arrived outside the French lines, and attacked towards Charleroi in an attempt to raise the siege, not knowing that the city had already fallen. The Allied attack was beaten off (battle of Fleurus, 26 June), and in the aftermath that failure the Austrians finally lost interest in any attempt to recover the Austrian Netherlands. By the end of July the Allied army had split in two, with the Austrians retreating east to the Rhine while the British and Dutch moved north to defend the Netherlands. The Austrians would never return to Belgium.