Dark Command

Dark Command is a 1940 Western film starring Claire Trevor, John Wayne and Walter Pidgeon loosely based on Quantrills Raiders during the American Civil War. Directed by Raoul Walsh from the novel by W.R. Burnett, Dark Command is the only film in which western icons John Wayne and Roy Rogers appear together, and was the only film Wayne and Raoul Walsh made together since Walsh discovered Wayne working as a prop mover, renamed him, and gave him his first leading role in the widescreen western The Big Trail a decade before.

Mary McCloud Claire Trevor marries a seemingly peaceful Kansas schoolteacher William Cantrell Walter Pidgeon, before finding out that he harbors a dark secret. He is actually an outlaw leader who attacks both sides in the Civil War for his own profit. After capturing a wagon loaded with Confederate uniforms, he decides to pass himself off as a Confederate officer. Her naive, idealistic brother Fletcher Roy Rogers joins what he believes is a Rebel guerrilla force. Meanwhile, Cantrells stern, but loving mother Marjorie Main refuses to accept any of her sons illgotten loot.A former suitor of Marys, Union supporter Bob Seton John Wayne, is captured by Cantrell and scheduled for execution. After being rescued by a disillusioned Fletcher McCloud, Seton and Mary Cantrell race to the town of Lawrence site of an actual infamous Quantrillled massacre to warn the residents of an impending attack by Cantrells gang. ........

Source: Wikipedia