One year ago, the city’s freedoms were curtailed with breathtaking speed. But the clampdown was years in the making, and many signals were missed.

I had never imagined that you could use this approach, Tam Yiu-Chung, the sole Hong Kong member of the top committee of Chinas legislature, said in a recent interview. Id heard about it, but there were so many difficulties with it.
By July 2017, when Hong Kongs elite gathered to celebrate the 20th anniversary of the territorys return to Chinese sovereignty, Mr. Xi was ready to raise the stakes.
It was his first visit to Hong Kong as Chinas top leader. Hours before tens of thousands kicked off an annual protest for greater democratic rights, Mr. Xi inserted a steely warning into his celebratory speech.
Threats to national sovereignty and security, or challenges to the central governments authority in Hong Kong, would cross a red line and will never be permitted, Mr. Xi said.
In Chinas top-down system, Mr. Xis words galvanized policymakers to look for new ways to defend that red line.
One influential adviser, Chen Duanhong, a professor of law at Peking University, submitted several internal reports about Hong Kong to Communist Party headquarters, including one about adopting security legislation. Around that same time, he wrote publicly that in a dire crisis, Chinese leaders could take all necessary measures to defend sovereignty, casting aside the fetters of lesser laws.
The will of the state must constantly respond to its environment of survival, he wrote, and then take decisive measures at crucial moments.