Shenzhen is a city that builds. In the 1980s, during China’s economic reforms, Deng Xiaoping declared the city a special economic zone, calling on migrants from across the country to move there to construct a metropolis from the ground up. They built highways, bridges, and the city’s first skyscraper, the fifty-story Guomao Building, at a rate of one floor every three days—a pace that came to be known as “Shenzhen speed.” They dredged ports, carved tunnels through bedrock, and raised glass towers on reclaimed land. They built factories that first made T-shirts, cardboard boxes, and plastic toys, then circuit boards, televisions, karaoke microphones, gaming consoles, and most of the world’s iPhones. By the late 2010s Shenzhen produced more than 90 percent of the world’s electronics, earning it the moniker “the Silicon Valley of hardware.” Today the city is home to the world’s largest makers of electric vehicles, telecommunications equipment, and consumer drones.…