PHOTOGRAPH BY BOBBY YIP/REUTERS

In the summer of 1996, the Chinese Communist Party erected a giant digital clock, fifty feet tall and thirty feet long, beside Tiananmen Square, which counted down the seconds until, as it said in large characters across the top, “The Chinese Government Regains Sovereignty Over Hong Kong.” After a century and a half under British colonial rule, Hong Kong’s restoration, in 1997, was a hugely symbolic moment for China’s national identity, an end to a history of invasion in which, as the Chinese put it, their land was “cut up like a melon” by foreign powers.

Under a deal brokered with the British, China agreed not to alter Hong Kong’s internationalized way of life—including freedom of expression, freedom of assembly, and other political rights not permitted on the mainland—for half a century. The theory was that, as mainland China continued to climb out of the poverty and political instability of the past, its leaders would gradually allow more political openness on the mainland. After a half century, or so the thinking went, the gap between the mainland and its reunited territory would have narrowed so much that they could mesh without much difficulty.

But, after nearly two decades, things are turning out differently. On Sunday, the Beijing government rejected demands for free, open elections for Hong Kong’s next chief executive, in 2017, enraging protesters who had called for broad rights to nominate candidates. China’s National People’s Congress announced a plan by which nominees must be vetted and approved by more than fifty per cent of a committee that is likely to be stacked with those who heed Beijing’s wishes. If that plan comes to pass, opposition figures who favor more democracy have little chance of making it onto the ballot. (As Boss Tweed liked to say, “I don’t care who does the electing, so long as I get to do the nominating.”)

The crisis, which will likely grow, is proving to be a test not only of Hong Kong’s political culture but also of which political ethic will prevail across China in the years ahead: globalism or nationalism, two fundamentally different conceptions of how China will relate to the rest of the world. Hong Kong takes pride in its role as Asia's original global city, a cultural and political mashup with a raucous, multilingual press corps and hot and noisy local politics—a largely borderless world of money, people, and ideas. Its courts rely on English common law, which is, in theory, free from political influence.

But, on the mainland, even as China’s economy has continued to grow and its population has become more integrated with the world, leaders have set new limits on political liberalization. They have concluded that greater democracy would threaten political stability and sovereignty, and they believe that China must instead adhere to its own centralized, one-party model. Last summer, as the scholar Sebastian Veg described, the Party circulated an internal directive to members that singled out seven “do not mention” topics: “democracy, universal values, civil society, market liberalism, media independence, criticizing errors in the history of the Party (‘historical nihilism’), and questioning the policy of opening up and reforms and the socialist nature of the regime.”

Hong Kong’s growing activist network, known as Occupy Central (named after the city’s downtown) has increasingly alarmed leaders in Beijing, and they now describe the activism as a brush fire that could sweep over the mainland. In a piece published on Saturday, the People’s Daily, the Communist Party mouthpiece, hinted about foreign agitators “attempting to turn Hong Kong into a bridgehead for subverting and infiltrating the Chinese mainland. This can absolutely not be permitted.”

In theory, China’s President, Xi Jinping, could have sought a middle road that would have opened up the nominating process enough to produce a competitive election. But, when the protests began earlier this year, Beijing worried that backing down would embolden further acts of resistance, not only in Hong Kong but also on the mainland. “If we yield because some people threaten to commence radical, illegal activities, it would only result in more, bigger illegal activities,” Li Fei, a mainland official, told Hong Kong lawmakers.

That is a strategy that points toward confrontation. Beijing chose the safer, short-term solution, but it left in place the ingredients for growing tension. Benny Tai, a law professor and opposition leader, said that the announcement opened a new “era of resistance.” “Today is not only the darkest day in the history of Hong Kong’s democratic development,” he told reporters. “Today is also the darkest day of one country, two systems,” a reference to the relationship between Hong Kong and the government in Beijing.

The most important questions are now up to the opposition: How far will pro-democracy activists go? Historically, Hong Kong’s political culture is loud and demonstrative, but not violent. The protesters have vowed to block Hong Kong’s financial district, in order to bring it to a standstill. But will it be a symbolic effort or a functional attempt to force a confrontation?

In turn, how will the Beijing-backed local government respond? Not long ago, it would have been unthinkable to imagine People’s Liberation Army vehicles on the streets of Hong Kong, but in the past quarter century the Party has shown that it is prepared to take whatever steps it deems necessary to tamp down public protests. On Sunday, hundreds of local police, and dozens of their vehicles, were arrayed around Hong Kong’s government headquarters. Last week, at least four P.L.A. armored personnel carriers were spotted in the streets.

Most important, if the confrontation becomes more acute, how will Hong Kong’s largely moderate middle class respond? So far, it has provided ambivalent support for the Occupy Central movement, fearing that unrest, even for popular ideas, could undermine the city’s business climate or invite harsher measures from Beijing. But how many of Hong Kong’s citizens will see a show of force as a reason to back down, and how many will see it as a reason to join the more radical pro-democracy camp?

The struggle over political values at the center of this crisis runs much deeper than the technical debate over Hong Kong’s elections. It is likely to get worse before it gets better. In a statement on Sunday, the Occupy Central activists described a sense of desperation, a belief that “all chances of dialogue have been exhausted and the occupation of Central will definitely happen.” It did not say when that occupation will begin.