The Last Samurai
An American military advisor embraces the Samurai culture he was hired to destroy after he is captured in battle.
Well thats what IMDB says the movie is about. Mostly its about Tom Cruise (Civil War hero and drunkard) being acted off the set by Ken Watanabe (Samurai leader and damn fine actor).
In fact if you ignore Cruise and treat him as a minor character, its a pretty good movie.
Since the basic plot is extremely similar to Kevin Costner's 'Dances with Wolves', this movie is sometimes referred to as 'Dances with Ninja'.