Brian Aherne, as the Emperor Maximillian, is the strongest thing going for this historical film depicting the failed attempt by Louis Napoleon to create a puppet government in Mexico. The rest of the casting is uneven at best. John Garfield is badly miscast as Diaz, as is that great character actor Donald Crisp. Paul Muni playing the Zapotac Indian, Benito Juarez, manages to just look stoic and sullen and is not called upon to do much acting. Maybe it's the makeup! Claude Rains and Gale Sondergaard are outstanding as Napoleon III and his queen Eugenie and they play at the devious political game with just the right amount of intrigue.
The film is historically correct and that is part of the problem. The filmmakers put every incident that led to the fall of Maximillian into the story and the film drags on and on. It's more information that we need to know.
There are mixed opinions on the Bette Davis portrayal of Empress Carlotta, the unstable wife of Maximillian. Hers is an interesting story but Davis may not have put enough incipient madness into her characterization.
On the whole,this is a pretty good history lesson with no Hollywood happy ending tacked on, that tells of a well meaning, gentle man who was badly used by the French emperor, sent to rule a people of whom he knew nothing, in a land where he was not wanted. And Aherne absolutely is perfect for the part.....he is the star of this film.