Complex sentence: He then fought throughout the great defensive campaign of 1814 until the last battle before Paris, from which he fought a skilful fighting retreat drawing back his forces to the commanding position of Essonne and inflicting high casualties on the enemy.
Split into simpler sentences: He then fought throughout the great defensive campaign of 1814 until the last battle before Paris. Marmont's forces fought a fighting retreat back to the commanding position of Essonne and inflicting high casualties on the enemy.