Hong Kong’s march toward an authoritarian future began with a single phrase in a dry policy paper. Beijing, the document declared, would wield "comprehensive jurisdiction” over the territory.

The paper, published in June 2014, signaled Chinese leader Xi Jinping’s determination to tame political defiance in the former British colony, which had kept its own laws and freedoms. But the words were dismissed by many as intimidating swagger that the city’s robust legal system and democratic opposition could face down.

Hong Kong now knows Xi’s ambitions with a stunned clarity. The paper marked the opening of a contest for control in the city, culminating in the sweeping national security law that few saw coming.