Protest marches and vigils are fairly common in Hong Kong, but what began on Friday and escalated dramatically on Sunday is unprecedented. Mass acts of civil disobedience were met by a shocking and swift police response, which has led to clashes in the streets and popular outrage so great that analysts can only guess at what will happen next.

What's going on in Hong Kong right now is a very big deal, and for reasons that go way beyond just this weekend's protests. Hong Kong's citizens are protesting to keep their promised democratic rights, which they worry — with good reason — could be taken away by the central Chinese government in Beijing. This moment is a sort of standoff between Hong Kong and China over the city's future, a confrontation that they have been building toward for almost 20 years.

This began with a movement called Occupy Central but escalated when police surprised them with force

On Wednesday, student groups led peaceful marches to protest China's new plan for Hong Kong's 2017 election, which looked like China reneging on its promise to grant the autonomous region full democracy (see the next section for what that plan was such a big deal). Protest marches are pretty common in Hong Kong so it didn't seem so unusual at first.

Things started escalating on Friday. Members of a protest group called Occupy Central (Central is the name of Hong Kong's downtown district) had planned to launch a "civil disobedience" campaign on October 1, a national holiday celebrating communist China's founding. But as the already-ongoing protesters escalated they decided to go for it now. On Friday, protesters peacefully occupied the forecourt (a courtyard-style open area in front of an office building) of Hong Kong's city government headquarters along with other downtown areas.

The really important thing is what happened next: Hong Kong's police cracked down with surprising force, fighting in the streets with protesters and eventually emerging with guns that, while likely filled with rubber bullets, look awfully militaristic. In response, outraged Hong Kong residents flooded into the streets to join the protesters, and on Sunday police blanketed Central with tear gas, which has been seen as a shocking and outrageous escalation. The Chinese central government issued a statement endorsing the police actions, as did Hong Kong's pro-Beijing chief executive, a tacit signal that Beijing wishes for the protests to be cleared.

You have to remember that this is Hong Kong: an affluent and orderly place that prides itself on its civility and its freedom. Hong Kongers have a bit of a superiority complex when it comes to China, and see themselves as beyond the mainland's authoritarianism and disorder. But there is also deep, deep anxiety that this could change, that Hong Kong could lose its special status, and this week's events have hit on those anxieties to their core.

This all goes back to a promise China made in 1997 — and might be breaking

This began in 1997, when the United Kingdom handed over Hong Kong, one of its last imperial possessions, to the Chinese government. Hong Kong had spent over 150 years under British rule; it had become a fabulously wealthy center of commerce and had enjoyed, while not full democracy, far more freedom and democracy than the rest of China. So, as part of the handover, the Chinese government in Beijing promised to let Hong Kong keep its special rights and its autonomy — a deal known as "one country, two systems."

A big part of that deal was China's promise that, in 2017, Hong Kong's citizens would be allowed to democratically elect their top leader for the first time ever. That leader, known as the Hong Kong chief executive, is currently appointed by a pro-Beijing committee. In 2007, the Chinese government reaffirmed its promise to give Hong Kong this right in 2017, which in Hong Kong is referred to as universal suffrage — a sign of how much value people assign to it.

But there have been disturbing signs throughout this year that the central Chinese government might renege on its promise. In July, the Chinese government issued a "white paper" stating that it has "comprehensive jurisdiction" over Hong Kong and that "the high degree of autonomy of [Hong Kong] is not an inherent power, but one that comes solely from the authorization by the central leadership." It sounded to many like a warning from Beijing that it could dilute or outright revoke Hong Kong's freedoms, and tens of thousands of Hong Kong's citizens marched in protest.

Then, in August, Beijing announced its plan for Hong Kong's 2017 elections. While citizens would be allowed to vote for the chief executive, the candidates for the election would have to be approved by a special committee just like the pro-Beijing committee that currently appoints the chief executive. This lets Beijing hand-pick candidates for the job, which is anti-democratic in itself, but also feels to many in Hong Kong like a first step toward eroding their promised democratic rights.

It's about much more than one election: democracy, Tiananmen, and an uncertain future

People in Hong Kong have long wondered whether the Chinese government, famous for its heavy-handed authoritarianism and its fear of democracy, would really allow Hong Kong to become fully democratic or even keep what freedoms it had under British rule. The 2017 election was going to be a test case. So when China began to break its promises for the election, it raised a very scary question: is Beijing just going to erode Hong Kong's freedoms a little bit, or is it going to impose the same dictatorial rule it uses in mainland China, one of the least free societies in the world?

So these protests aren't just about Beijing's plan to hand-pick candidates for the 2017 election, they're about whether Hong Kong will remain fundamentally free, an ongoing and open-ended question that will continue for years no matter how these protests resolve.

The other thing you have to understand is that the memory of the 1989 Tiananmen Square massacre, in which the Chinese military mowed down 2,600 peaceful pro-democracy protesters in Beijing and other cities, looms awfully large in Hong Kong. While Hong Kong was unaffected by the massacre (it was under British rule at the time), the city holds an annual vigil in memory of the event, which has been so heavily censored in China itself that many young people have never heard of it.

Hong Kongers feel they have a responsibility to keep memory of Tiananmen for the fellow Chinese who cannot, but they also earnestly fear that it could happen to them. So that is a big part of why Hong Kong's residents are so upset to see their police donning military-like uniforms and firing tear gas this weekend; it feels like an echo, however faint, of 1989's violence. And in July, when Hong Kong residents protested the Chinese "white paper" implicitly arguing that China could revoke their freedoms, some pro-Beijing officials seemed to warn, even so subtly, that China's military could hypothetically put down any unrest in Hong Kong.

The protesters and Beijing are both hoping to force Hong Kong's divided public to decide on their future

This crisis comes in the middle of a political division among the citizens of Hong Kong, who embrace their freedoms but also tend to be conservative, over their future as part of China. Some are okay with integrating with the rest of China, or at least accept it as inevitable and don't want to kick up too much of a fuss, while some want to fight for democracy and autonomy. (There are other layers to this debate, such as Chinese nationalism versus Hong Kong exceptionalism; there's also a strong law-and-order constituency.)

You saw that split in a mid-September opinion poll asking Hong Kongers whether or not they should accept Beijing's plan for the 2017 election: 48 percent said Hong Kong should reject the plan as insufficiently democratic, while 39 percent said they should accept the deal despite the tradeoffs.

That public opinion split among Hong Kong residents is what makes this week really important. The protesters were hoping to galvanize public opinion against Beijing's plan for the 2017 election, and against China's more gradual erosion of Hong Kong's freedoms. But Beijing (and Hong Kong's pro-Beijing chief executive) seemed to hope that, by unleashing this highly unusual crackdown, they could nudge Hong Kong's ever-conservative mainstream against the protesters and in favor of the status quo.

In other words, both the pro-democracy protesters and Beijing are hoping to force Hong Kong's public to choose whether or not to accept, at a fundamental level, China's growing control over Hong Kong politics. If the public tacitly accepts Beijing's terms for the 2017 election, it will likely be taken as a green light for more limits on Hong Kong's democracy and autonomy, however subtle those limits end up being. But if Hong Kong residents join the protesters en masse, they will be rejecting not just the 2017 election terms, but the basic terms of Hong Kong's relationship with the central Chinese government.

It is simply too early to tell which direction these protests will go. Although early indications suggest that thousands of residents began joining the students in protest on Sunday, it's not clear if this will grow significantly larger, as is probably necessary to force change, or will fizzle out under police pressure. However it resolves, though, this is a potentially decisive moment for Hong Kong and the uncertainty that has hung over its future ever since 1997.