High school geographic population migration

The main reason for the title is that it is different from the other three pictures.

Abd's "Going to Kanto, Going to the Western Regions and Going to South Asia" is three major immigration waves in China's modern history, all of which have the same reason: "There are few land resources available for emigration or serious natural disasters", that is, too many people make a living from it and too few people; C occurred after the Yongjia Rebellion in the Jin Dynasty, apparently to escape the war.