Complex sentence: In 1792 he took part as a volunteer in the campaign of Champagne; in 1793 he assumed, in conformity with the Revolutionary fashion, the pre-name of Atticus, and became secretary to Clavière, then finance minister.
Split into simpler sentences: In 1792 he took part as a volunteer in the campaign of Champagne. In 1793 he assumed, in keeping with Revolutionary fashion, the pseudonym "Atticus"; and he became secretary to Clavière, then finance minister.