What is the fourth population movement?

What is the fourth population movement?

The fourth population movement and the last one so far is from the end of the 1960s till now. In this period, the population flow is from the Northeast and Central North to the West and the South, that is, to the sunbelt areas. Population in the South increased by 55.47% between 1960 and 1990 and population in the West increased by 88.17% in the same period.