June 4, 1989, was a seminal day for China’s faithful, as the Chinese government massacred thousands of pro-democracy demonstrators in Beijing’s Tiananmen Square. The same day, Communist Party leaders watched as pro-democracy candidates in Poland supplanted Communist rule—with Pope John Paul II’s indispensable support. Together the events jolted Beijing into tightening its control over religion.

Post-Tiananmen, Christian groups were made to register with state “patriotic” associations or risk punishment as “evil cults.” Anxious...