He then attached himself to the Girondist party and, on 15 March 1792, became the French minister of foreign affairs. Dumouriez then selected Pierre LeBrun as his first officer for Belgian and Liégeois affairs. The relationship between the Girondists and Dumouriez was not based on ideology, but rather based on the practical benefit it gave to both parties. Dumouriez needed people in the Legislative Assembly to support him, and the Girondists needed a general to give them legitimacy in the army. He played a major part in the declaration of war against Austria (20 April), and he planned the invasion of the Low Countries. His foreign policy was greatly influenced by Jean-Louis Favier. Favier had called for France to break its ties with Austria. On the king's dismissal of Roland, Clavière and Servan (13 June 1792), he took Servan's post of minister of war, but resigned it two days later on account of Louis XVI's refusal to come to terms with the National Constituent Assembly, and went to join the army of Marshal Luckner. After the "émeute" of 10 August 1792 and Lafayette’s flight, he gained appointment to the command of the "Army of the Centre". At the same moment, France's enemies assumed the offensive. Dumouriez acted promptly. His subordinate Kellermann repulsed the Prussians at Valmy (20 September 1792), and Dumouriez himself severely defeated the Austrians at Jemappes (6 November 1792). After these military victories, Dumouriez was ready to invade Belgium to spread revolution. He was a true revolutionary in the sense that he believed that nations which had undergone a revolution, in this instance France, should give aid to oppressed countries. As his plans were largely limited to Belgium, this tunnel vision sometimes prevented him from acting in the most logical fashion as a commander.