Complex sentence: Survivors from the citadel were executed, artisans and craftsmen were sent back to Mongolia, young men who had not fought were drafted into the Mongolian army and the rest of the population was sent into slavery.
Split into simpler sentences: Survivors from the citadel were eventually defeated and executed, while artisans and craftsmen were sent to Mongolia. Young men who had not fought were drafted into the Mongolian army and the rest of the population was sent into slavery.