Mohawk (1956)

Plot from the Imdb says
Jonathan Adams, an artist on assignment for a Massachusetts society to paint frontier scenes, is away from Boston so long that his fiancée, Cynthia Stanhope, chaperoned by her Aunt Agatha, travel to Fort Alden seeking him. She finds him using Greta Jones, daughter of storekeeper Clem Jones, as a model. Butler, a fanatic, is seeking to instigate an Indian war so that he might gain control of the whole Mohawk valley. Mohawk Chief Kowanen holds his tribe in check but impatient warrior Rokhawah goads tribe-members into raiding the fort for guns. Onida, Kowanen's daughter, agrees to let the raiders into the fort after sundown and finds herself trapped in Adams' quarters after the raiders escape. He smuggles her out the next day and her father is grateful. Onida and Adams fall in love. Butler kills Kowanen's son, Keoga, and this prods the chief into declaring war against the whites, and even Adams is taken prisoner.