When did Napoleon achieve his greatest victory ?
Territories allied with the French included : the Kingdom of Spain ( under Joseph Bonaparte , Napoleon 's elder brother ) the Kingdom of Westphalia ( Jérôme Bonaparte , Napoleon 's younger brother ) the Kingdom of Naples ( under Joachim Murat , husband of Napoleon 's sister Caroline ) the Principality of Lucca and Piombino ( under Elisa Bonaparte ( Napoleon 's sister ) and her husband Felice Baciocchi ) ; and Napoleon 's former enemies , Prussia and Austria .