Lone Star is about history and how history can either be a prison or how it can set us free. The characters in the movie start out bound by their history. Their histories, familial and cultural, determine a course of action for the characters living in present day Rio County. By the end of the movie, these characters have come to grips with their own personal history. Their personal history no longer dictates their actions.
Sam Deeds is the current sheriff of Rio County and is plagued by his legendary father, who also was a sheriff. Sam is a reluctant sheriff and was elected by the townspeople who hoped he would be like his father. Sam's investigation into the murder of Charley Wade is driven by his history with Buddy: he's not interested in learning the "truth" but instead to shatter the legendary status of his father. The revelations through his investigation help to form a more complete history of Buddy Deeds for Sam; he no longer has the skewed and inaccurate picture formed from his own personal experiences with Buddy Deeds.
Col. Delmore Payne works his way up through the structured institution of the U.S. Army as a way to forget his estrangement with his father. He tries to instill this discipline in Chet's (his son) life. Col. Payne wants to be a strong influencing force in his son's life to compensate for his father's lack of involvement in his own life. Chet develops his own relationship with Col. Payne's father, Otis, and thus brings Otis back into his father's life. By the end of the movie Col. Payne is beginning to form a relationship. Once he lets go of the history between him and his father, he becomes a more of a father and less of a disciplinarian to Chet.
Mercedes Cruz, mother of Pilar, is an immigrant from Mexico trying to free herself of her dirty Mexican past and assimilate into American culture. She has become the most successful Mexican-American businesswoman in the town. She owns a Mexican restaurant and always scolds her workers when they speak Spanish instead of English. She lives near the Mexican border and has a good view of Mexicans trying to cross the border illegally. Anytime she sees this, she calls the Border Patrol to report them. This is in direct contrast to her own past, where she crossed into the U.S. as an illegal immigrant. Her moment of "freedom" comes when she helps the fiancée of an employee. She breaks her leg trying to cross the river into the U.S. and Mrs. Cruz calls in a favor to a local doctor.
The romance between Sam and Pilar is the most controversial example of history colliding with present. Sam and Pilar were high school sweethearts and were reunited after Sam came back to Rio County. Through the course of his investigation into the murder of Charley Wade, Sam stumbles across some explosive history that could change their relationship permanently. This is controversial and sure to spark extreme opinions, but I think their final decision follows in the theme of the movie. They break free of the chains of history to try and forge ahead in the present.