Waves of sometimes violent protests have swept across Hong Kong this year, triggered initially by the introduction of an extradition bill that residents see as China's latest attempt to erode their political freedoms.

So how did things get this bad? CBC News explains.

Why are there tensions?

Hong Kong, a major Asian commercial hub, returned to China in 1997 after 156 years of British rule.

That transfer of power on July 1, 1997 — known as "the handover" — came with certain conditions designed to guarantee Hong Hong "a high degree of autonomy."

Under the "one country, two systems" principle, Hong Kong is considered a Special Administrative Region of China and maintains an independent legislative system and a legal system based on British common law that should guarantee property rights and a fair trial in criminal cases. But Hong Kongers have long accused Beijing of encroaching on this autonomy since the handover, spurring protests and unrest.

An extradition bill proposed by the the Hong Kong government this year triggered the latest wave of demonstrations that began back in late April, which have gradually grown violent as protesters make broader democratic demands.

What is the extradition bill?

The controversial extradition bill was proposed on April 3, ostensibly as a response to the Hong Kong government's inability to extradite a Hong Kong man to Taiwan after he allegedly killed his girlfriend on a trip there. But proposed amendments to the bill would also allow Hong Kong to send people to the mainland to face charges.

Protesters douse tear gas with water at a demonstration on Sunday while rallying against the extradition bill. (Billy H.C. Kwok/Getty Images)

Critics contend that defendants extradited to mainland China may not have access to a fair trial in the judicial system there and that Beijing could also use the law to crack down on Hong Kong dissidents.

Intense protests then followed on June 9 as hundreds of thousands of pro-democracy demonstrators were joined by civil servants and others, including business professionals. The bill was declared "dead' as of last month by Hong Kong Chief Executive Carrie Lam but she didn't withdraw it, and protests have continued.

Who is the Hong Kong leader?

Lam is Hong Kong's chief executive — a position selected by a 1,200-member committee, with seventy members belonging to the Hong Kong legislature and the rest representing different sectors like business and agriculture.

Observers say Beijing heavily lobbies in favour of a particular candidate ahead of an election. Many see the process as undemocratic, as it is unfairly weighted toward representatives in business and trade, who commonly vote in accordance with the wishes of Beijing.

Hong Kong Chief Executive Carrie Lam speaks during a news conference on Aug. 5 about protests against her extradition bill, for which she has apologized but not completely withdrawn. (Anthony Kwan/Getty Images)

As Beijing's choice , Lam landed the job in 2017 despite trailing runner-up John Tsang in public opinion polls. She's the first woman to lead Hong Kong, but many view her as Beijing's puppet.

Protesters have called for her resignation in light of her introduction of the extradition bill.

Lam said last month that the bill has failed but has refused to withdraw it completely, leading to accusations that she's simply stalling for another chance to ram it through.

How might China respond?

Beijing has labelled the latest protests an "existential threat" to Hong Kong and an act of "terrorism" after local authorities shut down the city's international airport on both Monday and Tuesday due to continuous demonstrations.

Passengers rest at the check-in counters in Hong Kong's international airport after all flights were cancelled Monday due to continuing protests. (Thomas Peter/Reuters)

China's military —​ the People's Liberation Army —​ ​​​​​​has a garrison of 6,000 soldiers in Hong Kong. Lam has the authority to request their help to "maintain social order."

If this happens, many fear a repeat of the 1989 Tiananmen Square incident, where the army cracked down violently on democratic protesters in Beijing. China has never disclosed how many people died in the clashes but human rights organizations have estimated the death toll to be between several hundred to several thousand.

Additionally, members of China's paramilitary People's Armed Police (PAP) recently marched and practised crowd control tactics at a sports complex in Shenzhen — a Chinese city located across the border from Hong Kong on Friday — in what some interpreted as a threat against the protesters.

What do protesters now want?

The core demands of the protests are for the extradition bill to be completely withdrawn and for Lam to resign.

But violent clashes have also prompted calls for investigations into police brutality and possible involvement by organized crime in beating back demonstrations.

The protests have also been an opportunity for a general airing of grievances against Beijing — including calls for democratic elections — fuelled by broader worries about the erosion of freedoms guaranteed under the "one-country, two-systems" formula.