Why are there so many Han people in Ningxia?

Most of the Han people in Ningxia fled to Ningxia because people from the north fled to avoid war and plague. The population source of Ningxia Hui Autonomous Region is very complicated. The Han population mainly comes from Shanxi, Henan and other regions. These people mainly fled to Ningxia from the mainland and other provinces and cities outside Ningxia, and finally settled in various cities and counties in Ningxia Hui Autonomous Region. This is the source of the Han population in Ningxia Hui Autonomous Region.