Complex sentence: Bon Marché was opened in 1852 by Aristide Boucicaut, the former chief of the "Petit Thomas" variety store, in a modest building, and expanded rapidly, its income going from 450,000 francs a year to 20 million.
Split into simpler sentences: Bon Marché was opened in 1852 by Aristide Boucicaut, the former chief of the Petit Thomas variety store, in a modest building. His venture expanded rapidly, its income growing from 450,000 francs a year to 20 million.