Critical pieces of China’s cutting-edge surveillance state share a connection. They came from America.

Some of the biggest names in U.S. technology have provided components, financing and know-how to China’s multibillion-dollar surveillance industry. The country’s authoritarian government uses those tools to track ethnic minorities, political dissidents and others it sees as a threat to its power—including in Xinjiang, where authorities are creating an all-seeing digital monitoring system that feeds into a network of detention...