“Every move in my own home is monitored,” Yang said, sitting behind black curtains that block him from the glare of police lights trained straight at his house. “Their surveillance makes me feel unsafe all the time, everywhere.”

Across China, tens of thousands of people tagged as troublemakers like the Yangs are trapped in a digital cage, barred from leaving their province and sometimes even their homes by the world’s largest digital surveillance apparatus. Most of this technology came from companies in a country that has long claimed to support freedoms worldwide: the United States.

Over the past quarter century, American tech companies to a large degree designed and built China’s surveillance state, playing a far greater role in enabling human rights abuses than previously known, an Associated Press investigation found. They sold billions of dollars of technology to the Chinese police, government and surveillance companies, despite repeated warnings from the U.S. Congress and in the media that such tools were being used to quash dissent, persecute religious sects and target minorities.

Critically, American surveillance technologies allowed a brutal mass detention campaign in the far west region of Xinjiang — targeting, tracking and grading virtually the entire native Uyghur population to forcibly assimilate and subdue them.