Estimated at 250 million people, China's migrant labor force is the largest in the world. Two main factors have contributed to its emergence in recent decades: first, the surplus labor made available by China's transition from a primarily agricultural economy to an export-oriented industrial economy since the 1980s; second, the rapid development along the coast that made it the logical destination for much of that surplus labor. These workers provided the country with a near-inexhaustible supply of cheap labor for unskilled manufacturing and infrastructure construction along the coast , which in large part sustained the country's economic miracle . Due to migrant workers' relatively replaceable nature (most are temporary contract workers and do not receive benefits that would tie them to their jobs long term) these laborers are the most sensitive to social or economic changes.