The Overland Telegraph (1929)

At the beginning of the Civil War, as federal troops start to build the first overland telegraph, Indians, who fear the wires, kill some of the linesmen. In response, Major Hammond, who oversees the troops, requests that President Abraham Lincoln send twenty thousand more soldiers to come to his aid. Lincoln grants Hammond's request, and sends along Capt. Allen, who is knowledgeable about Indians. At his new post, Allen discovers that a Confederate spy has been fomenting trouble with the Indians. Allen eventually uncovers the spy, makes peace with the Indians and wins the love of Dorothy, a young woman who lives at the post.