Complex sentence: As André Masséna's second-in-command he was present at the battle of Fuentes d'Onoro, but Napoleon never detached him for very long, and in 1812 he commanded the Guard Cavalry at the Battle of Borodino and in the retreat from Moscow.
Split into simpler sentences: As André Masséna's second-in-command he was present at the battle of Fuentes d'Onoro, but Napoleon never detached him for very long. In 1812 he commanded the Guard Cavalry at the Battle of Borodino and in the retreat from Moscow.