What are the historical reasons that caused the ancient Han people to move to the frontier?

1. Poor peasants who have no land or little land go to the frontier to cultivate land to make a living (for example, crossing the Kanto and going west).

2. Soldiers set up fields and defended the border to go to the frontier (for example, the armies of past dynasties set up fields).

3. The government's policy on frontier development (for example, in the Qing Dynasty, Han residents were forbidden to go to Northeast China and Mongolia to make a living, and then the ban was lifted due to the invasion of these areas by foreign powers).

4. The war caused the exiles to go to underdeveloped areas to open up new cultivated land (such as the chaos in the late Han Dynasty, the southern crossing of Yongjia, the Anshi rebellion, and the change of Jingkang).