A residential development in Nanchang, China. Decades of overdevelopment in China have yielded cities full of empty apartment blocks. Photograph: Qilai Shen/The New York Times For more than a quarter-century, China has been synonymous with relentless development and upward mobility. As its 1.4 billion people gained an appetite for the wares of the world – Hollywood movies, South Korean electronics, iron ore mined in Australia – the global economy was propelled by a seemingly inexhaustible engine. Now that engine is sputtering, posing alarming risks for Chinese households and economies around the planet. Long the centrepiece of a profit-enhancing version of...