Once Upon a Time in the West (1968) on Netflix

A prostitute leaves her job and town to come to a part of the west with a long history of violence and avarice in order to join her new husband. When she finds him brutally murdered by an unknown assailant (Frank), she gets help from a mysterious harmonica player with a great talent for working with guns. He knows it's Frank, whom he's already been looking for himself for a long time (for an undisclosed purpose). While "Harmonica" continues his hunt for Frank, another outlaw, Cheyenne, also seeks Frank, killing his people to find him for his own reasons.