After the declaration of war by France against the Archduchy of Austria (1792) and the declaration against Mainz on 21 July 1792, Comte de Custine was given command of the Army of the Rhine to replace Nicolas Luckner, and in September occupied the southern Rhineland about the cities of Speyer and Worms. The regiments of the Duke of Nassau left the Fortress of Mainz on October 5.
