(CNN) Hong Kong is facing a major political crisis amid repeated street protests and mass demonstrations. What started as a movement against a controversial law has expanded into something much bigger.

Over the past few months, the demonstrations have evolved from millions marching through the streets , to groups of protesters in hard hats storming government headquarters and shutting down the city's international airport for two days. While the majority of protesters have been peaceful, frustration is building on all sides.

Protesters are now demanding greater democracy and an inquiry into alleged police brutality during past demonstrations. Hong Kong's billionaires are calling for order . And as unrest intensifies, Beijing's tone is becoming increasingly heated.

Here's what you need to know:

What's the history here?

Hong Kong belongs to China, but it has its own currency, political system and cultural identity. Many Hong Kong residents don't see themselves as Chinese, but rather as Hong Kongers.

That difference goes back generations; the city was a colony and territory of the United Kingdom for more than 150 years, until the British handed it back over to China in 1997. Today, Hong Kong's legal system still mirrors the British model, prizing transparency and due process.

A policy dubbed "one country, two systems," enshrines this uniqueness. Under the policy, Hong Kong's maintains a de-facto constitution, known as the Hong Kong Basic Law. It guarantees freedoms that are unavailable to Chinese mainlanders, such as the right to protest, the right to a free press and freedom of speech.

One of the tenets in the Basic Law is that Hong Kong has the right to develop its own democracy, and previous Chinese officials pledged that the central government in Beijing wouldn't interfere with that. But in recent years, Beijing has repeatedly reinterpreted the Basic Law -- now it says it has "complete jurisdiction" over Hong Kong.

The Basic Law states that Hong Kong "shall safeguard the rights and freedoms of the residents" for 50 years after the handover. But many residents say mainland China is already starting to encroach on those rights.

This perceived threat to Hong Kong's rule of law has led to the regular confrontations which has seen hundreds of protesters arrested so far.

Protesters stormed and partially sacked Hong Kong's legislature.

What are the protesters demands?

In early August, violent outbreaks at Hong Kong airport set a newly combative tone , with protesters attacking and temporarily detaining two people.

Protests began in March, but they kicked off in earnest in June. They were sparked by widespread opposition to a now-shelved extradition bill, but have since expanded to demands for full democracy and police accountability.

Protesters have also been riled by recent allegations of police brutality. After a female protester was injured in the eye during clashes with police who were trying to disperse crowds, protesters at the airport wore eyepatches in reference to the woman's injury.

As the protest movement is leaderless, not everyone has the same goals in mind. But in general, five main demands have emerged: withdraw the bill, for leader Carrie Lam to step down, an inquiry into police brutality, for those who have been arrested to be released, and greater democratic freedoms.

On the protest front lines, demonstrators have confronted police and been targeted by stick-wielding men in white , whom some accuse of collaborating with the government. But while many Hong Kongers have been inconvenienced by transport shutdowns and other travel disruptions, there is little sense of danger in the rest of the city.

Why did protesters target the airport?

Many activists had come to view Hong Kong's international airport as something of a safe protest space away from the streets, where clashes between demonstrators and police have become commonplace.

But that changed after police clashed in the airport -- and authorities issued an injunction to prevent future protests there.

The airport, which is one of the busiest in Asia, had emerged as a key protest target as anti-government demonstrators looked to take their message directly to the international community.

At the airport in August, leaflets in Chinese, English, French, Korean, Japanese and other languages were handed out to arriving international visitors, explaining the causes of the unrest -- as protesters see it -- and the demands of the opposition movement.

The airport, which is one of the busiest in Asia, has emerged as a key protest target.

Nearly 1,000 flights were affected by the protests in early August, according to the CEO of the Hong Kong Airport Authority. A court has since issued an injunction which restricts people from accessing the airport.

What does this mean for Hong Kong's economy?

While mainland China is Hong Kong's most important trading partner, the city is an international business and financial hub, and the economy is already showing signs of hurting as a result of the protests.

Companies have already reported "serious consequences from the disruption," including lost revenue, disrupted supply chains and shelved investments, the American Chamber of Commerce in Hong Kong said in June.

Businesses in Hong Kong, both international and local, have also faced pressure and accusations of acting in concert or sympathizing with the protesters. Cathay Pacific, Hong Kong's flagship carrier and a major local employer, has been ordered by Chinese aviation authorities to ban staff who take part in protests from traveling to China.

Canceled flights are terrible news for companies operating in the financial hub. More than 74 million passengers traveled to and from the airport last year. It handles 1,100 passenger and cargo flights each day, and serves about 200 destinations around the world.

Companies have already reported "serious consequences from the disruption."

The airport contributes 5% to Hong Kong's GDP, directly and indirectly, said Frank Chan, Hong Kong's transport secretary, in May.

Experts worry that travelers will now avoid Hong Kong. "This is a disaster for Hong Kong that will cost tens of millions of dollars," said Geoffrey Thomas, editor in chief and managing director of AirlineRatings.com, a website that monitors airlines.

What is the government saying?

Officials in both Hong Kong and Beijing are increasingly critical of the protests.

In China, coverage of the protests has shifted from censorship to focus on clashes and disorder, with protestors labeled as "violent mobs" and "criminals."

Yang Guang, a spokesman for the Hong Kong and Macao Affairs Office, China's top body in charge of affairs in the city, said the protests showed "signs of terrorism" and suggested that they were the real threat to rule of law.

"Hong Kong's radical demonstrators have repeatedly attacked police officers with extremely dangerous tools," he said. "They have already constituted serious violent crimes and have begun to show signs of terrorism. This is a gross violation of the rule of law and social order in Hong Kong, which is endangering the lives and safety for Hong Kong citizens."

The escalating rhetoric has sparked fears that China could be mulling an intervention of force.

In an interview with CNN, Max Baucus, former US ambassador to China, described the challenge that protestors posed to China's central government.

"If Beijing thinks they can just jam a solution down the protesters' throats, that's not going to work, and I think they know that and trying to figure a way out," he said.

"Don't forget. China is very conservative. It's hard for China to deal with matters like this -- they are used to having their own way. This has been difficult for them. They're not nimble. They don't have a big diplomatic core like the United States does for example. This is tough for them."

What are other countries saying?

US President Donald Trump called for calm. He claimed that US intelligence showed "the Chinese Government is moving troops to the Border with Hong Kong. Everyone should be calm and safe!" China already regularly maintains a troop presence near the Hong Kong border.

Meanwhile, British MPs have expressed concern of the deteriorating situation. MP Tom Tugendhat, chair of the UK government's House of Commons Foreign Affairs Committee, said the UK should consider extending "full citizenship rights to the HK Chinese".

"This should have been done in 1997 and is a wrong that needs correcting," Tugendhat tweeted.

UK Foreign Secretary Dominic Raab said he is concerned by "what's happening in Hong Kong and the worrying pictures of clashes between police and protesters."

"As I said to Carrie Lam during my call last week, we condemn the violence and encourage constructive dialogue to find a peaceful way forward," Raab tweeted.