The national security law China imposed on Hong Kong a year ago Wednesday was much more than a piece of legislation: It showed Beijing was now running the show in the former British colony.

The measure — enacted with immediate effect, and without public debate — has radically transformed the political and legal landscape of a financial center long known for its consistent application of the law. From scrubbing school curriculums to censoring films to denying some suspects the right to jury trials, the broad use of the legislation has left many people guessing about China’s new red lines.

The sweeping change, seen clearly by the Apple Daily’s disappearance from newsstands and the erasure of once-common protest slogans, undercuts Chief Executive Carrie Lam’s assurances that the measure would "only target an extremely small minority of illegal and criminal acts.” Tens of thousands of Hong Kong residents have sought to relocate to places like Canada and the U.K., and more than 40% of members surveyed last month by the local American Chamber of Commerce branch said that they were thinking about leaving.