Complex sentence: After Buck is beaten by Hal, Thornton recognizes him to be a remarkable dog; disgusted by the driver's treatment of Buck, Thornton cuts him free from his traces and tells the trio he's keeping him, much to Hal's displeasure.
Split into simpler sentences: After Buck is beaten by Hal, Thornton recognizes him to be a remarkable dog. Disgusted by the driver's treatment of Buck, Thornton cuts him free from his traces and tells the trio he's keeping him, much to Hal's displeasure.