Complex sentence: At sixteen, Horn headed to the American Southwest, where he was hired by the U.S. Cavalry as a civilian scout under Al Sieber and became involved in the Apache Wars, aiding in the capture of warriors such as Geronimo.
Split into simpler sentences: At sixteen, Horn headed to the American Southwest, where he was hired by the U.S. Cavalry as a civilian scout under Al Sieber. He served during the Apache Wars, aiding in the capture of warriors such as Geronimo.