Shanghai and Xinjiang used to be two sides of the China coin.

Shanghai was the glamorous China — with skyscrapers, art deco apartments and a thriving middle class that shopped in Paris and strolled around Kyoto.

Xinjiang was the dark China. The western frontier region, twice the size of Texas, is home to more than 10 million Muslim ethnic minorities who have been subject to mass detentions, religious repression and intrusive digital and physical surveillance.