the Han Emperor Wu sent 2 armies to punish a Greek-Persiany-Indian kingdom in central asia for killing an envoy as well to force them to sell him the horses they had (a breed the chinese referred to as 'heavenly horses'). the first had issues with supply but the 2nd got the job done; made up of 60k penal recuits and mercenaries (collectively called 惡少年, literally meaning "bad boys")