Because the film shows a number of Maximilian's generals to be Mexican, many viewers attribute it to typical Hollywood historical distortions. It is, however, indeed accurate. It's a little-known fact that, although Maximilian was eventually overthrown and executed by Mexican revolutionaries, there were more Mexicans fighting on Maximilian's side than against him. This was due in large part to the Catholic Church's strong support of the French occupation of Mexico and its encouraging of Mexican Catholics to fight against the revolutionary forces by joining Maximilian's army, which they did in large numbers.
Extensive research was done to provide accuracy. The writers had a bibliography of 372 books. Art director Anton Grot made 3,643 sketches from which 7,360 blueprints were prepared for exterior and interior settings. A complete Mexican village was built on the Warner Bros. ranch in the San Fernando Valley.
Benito Juarez was only 4ft 6ins tall (1.37 m).
According to Brian Aherne, the film was to have been called 'Phantom Crown,' after the novel by Bertita Harding which was one of the sources for the script. However, Muni had a clause in his contract that permitted him to insist that the name of his character appear in the title.
In a 1963 edition of BBC Radio's "Frankly Speaking" series Bette Davis claimed Paul Muni added 80 pages of script himself to bolster his role in the film.