A "cultural" insert,at the beginning of this western,tells us it's loosely based on historical facts:The war between Maximilian von Habsburg (abetted by Napoleon the Third ,who made one of his biggest mistakes in this Mexican adventure)and Benito Juarès,who was a genuine hero for Mexicans.
Loosely is the word indeed.The villain is French,a Max and Nap's spy,but,as far History is concerned ,everything stops here.All that remains is par excellence routine western:two brave heroes(Payne and O'Keefe,the eagleS) ,one gorgeous heroine(Fleming),a baddie,and a patriot general (Tomas Gomez,who sadly resembles more Zorro's Sergeant Garcia than a dashing officer).Thanks to the three leads,the movie is watchable,and boasts,as a highlight ,a sadistic scene of quartering between two mustangs.
However,people who saw the lines at the beginning and who wish to see something "historical",should catch William Dieterle's "Juarez" (1939) with Paul Muni and Bette Davis.