Liu Lang, a Chinese migrant worker, left his rural hometown in Sichuan Province two decades ago to work in the factories of the southern province of Guangdong, China’s manufacturing powerhouse. Now, he is moving back. “I worked my way up from a basic worker to a department head. And my career basically ended today,” Mr. Liu said on the train leaving Guangdong. Factories in Guangdong have been hit hard by the slowing economy, and many of them have closed, including the shoe factory where Mr. Liu worked.