Workers found it more worthwhile to stay in third tier cities than to migrate back to tier 1 cities on the coast, said Ira Kalish, a director of global economics at Deloitte.

FORBES: In Coastal China, A Labor Shortage

Hence, in Japan, when a wealthy man died, the eldest son inherited all, generally land, and the younger siblings, who were equally educated, tended to migrate to the cities and transferred their allegiance to the emperor rather than their families.

FORBES: Why China Is Finally Abandoning Its One Child Policy

It'll require changes to policies that restrict the ability of people to migrate permanently to the cities.

BBC: Can Wuhan's state-owned giants adapt?

Millions of children in India migrate from villages to cities every year, in search of job opportunities.

BBC: Family of gang rape accused 'made infamous' in home village

The country's State Forestry Administration estimates that desertification affects 400 million Chinese, many of whom lose the ability to farm their land or graze their animals and join the ranks of the tens of millions of internal environmental refugees, who often migrate to the big cities in search of new homes and jobs.

CNN: Economic miracle, environmental disaster

Many people must migrate for jobs, mostly from rural areas to the margins of cities and shanty towns.

BBC: By Sarah Shenker and Elinor Shields