What nationality are the southerners of the Mongolian Empire?

Southerners are the most ethnic-conscious group among the Han people, and they have strong economic and military strength to resist the invasion of foreign enemies, so they were conquered by the Mongols at the latest, which made the Mongols slaughter the southern Han people on a large scale after the Southern Song Dynasty. Due to the late surrender, southerners have the lowest value to be used by Mongols, so they have the lowest status. "