Soldier Blue (1970) on Netflix

While riding through the Cheyenne territory transporting a safe to Fort Reunion and protecting the white woman Cresta Marybelle Lee, who had lived in a Cheyenne village for two years and sympathize with them, the twenty-two men of the cavalry are attacked by the Indians. Only Cresta and the naive, idealistic and clumsy private Honus Gent survive, and together they walk to Fort Reunion, where Cresta is supposed to meet her fiancé Lieutenant McNair. Along their journey, Honus protects Cresta against Kiowa Indians, destroys the shipment of a trader of weapons and falls in love for Cresta, but he does not believe in Cresta words that the Cheyenne village is peaceful. When the cavalry attacks, he witnesses the hideous massacre of five hundred peaceful Cheyenne, more than half composed of women and children, and realizes that Cresta was telling the truth.