Why did Baldwin and McMurdo dislike each other?

During this “story within a story," we learn that Douglas once bore the name “Jack McMurdo," and that he was part of a notorious gang in the United States, which was not unlike the Mafia. Teddy Baldwin is young and hotheaded brother who wants to marry Ettie and resents McMurdo getting in his way. He continually butts heads with McMurdo; however, he grudgingly accepts him, until his true identity is revealed. He tracks McMurdo to England and tries to kill him; instead, McMurdo/Douglas kills Baldwin in self-defense.