Complex sentence: He fought again under Crook in the campaign against the Chiricahua Apache in the Sierra Madre of Mexico in 1883 and his last military duty was as an advisor during the pursuit of Geronimo in Mexico in 1885.
Split into simpler sentences: He fought again under Crook in the campaign against the Chiricahua Apache in the Sierra Madre of Mexico in 1883. His last military service was as an advisor during the pursuit of Geronimo in Mexico in 1885.