Complex sentence: He withdrew with the ex-emperor and a few other trusty followers to Rochefort, and it was Las Cases who first proposed and strongly urged the emperor to throw himself on the generosity of the British nation.
Split into simpler sentences: He withdrew with the ex-emperor and a few other trusty followers to Rochefort. It was Las Cases who first proposed and strongly urged the emperor to throw himself on the generosity of the British nation.