By the declaration of Pillnitz (1791), Leopold II, brother of the French queen, had laid the basis of the first coalition and manifested his intention of intervening in favour of Louis XVI. After his death (1792) Francis II pursued a still more aggressive policy towards the Revolution, and the Girondins, who had just come into power, obliged the King of France to declare war against Austria. The first attacks against Belgium were easily repulsed by the imperial troops, commanded by national leaders, but the victory of Jemappes (November 6th), won by Dumouriez with the help of a Belgian legion, opened the Belgian provinces to the revolutionary troops. General Dumouriez was a moderate and intended to remain faithful to the principles of liberty. He issued a proclamation, approved by the Convention, declaring that his soldiers were coming as allies and as brothers. When, on November 14th, he was offered the keys of Brussels by the magistrates, he refused them, saying: "Keep the keys yourselves and keep them carefully; let no foreigner rule you any more, for you are not made for such a fate." Greatly impressed by the warm reception given him in Mons and Brussels by the Vonckists, he did not realize that the country was far from being unanimous. The French general declared the Scheldt open, in accordance with a decree of the Republic which had proclaimed the freedom of the river.
While the Belgians hesitated to declare a Convention and to organize themselves according to the Republican régime, they began to feel the first effects of the occupation. The French army, in the region of Liége, lived only on requisitions. Cambon had presented to the Convention (December 1792) a decree suppressing all distinctions and privileges in the conquered territories, these being replaced by the sovereignty of the people. This sovereignty being without expression in Belgium, the provinces were practically administered by a number of Jacobin Commissaries, whose most important task was to confiscate the goods of the nobles and of the clergy and to enforce the circulation of the revolutionary paper money (assignats). These measures provoked a reaction in favour of Statism, and the conservatives obtained an overwhelming majority in the elections held in December. Meanwhile, England and the United Provinces, alarmed by the progress of the French in the Netherlands, had joined the first coalition (January 1793), and the Jacobins, dominating the Convention, had entered upon an annexationist policy, nothing short of the left bank of the Rhine being able, according to them, to secure France against the attacks of the reaction. In order to appease the scruples of the French moderates, the Jacobins endeavoured to provoke manifestations in favour of annexation in the Belgian provinces. A regular propaganda was organized by the Clubs. Orators, wearing the scarlet hood and armed with pikes, addressed the crowds in the market-places. The deputy Chepy, who had taken the leadership of the movement, declared that he was determined to obtain reunion by "the power of reason, the touching insinuations of philanthropy and by all means of revolutionary tactics." On many occasions crowds driven into a church were surrounded by armed "Sans Culottes" and obliged to manifest their attachment to the Republic by loud acclamations. In March 1793 a rising was imminent, ten thousand armed peasants being already concentrated near Grammont. It was prevented, at the last moment, by the return of Dumouriez, who ordered Chepy to be arrested, liberated hostages and enforced the restitution of the spoils taken from churches and castles. In a letter to the Convention, he protested against the mad policy pursued by the Jacobin Commissaries, and adjured them to read through the story of the Netherlands, where they would find that the good will of the Belgian people could never be obtained by force.