Complex sentence: With the hangman and a local posse on their trail, Madrid meets with his gang who later rob Bierce's stagecoach because of Reece's belief that Bierce holds an invaluable object.
Split into simpler sentences: With the hangman and a local posse on their trail, Madrid meets with his gang. They later rob Bierce's stagecoach because of Reece's belief that Bierce possesses an invaluable object.