In Hong Kong, why did an estimated 1 million or more turn out to protest Sunday? The problem was a proposed amendment to criminal legislation — if the measure passes, the Hong Kong government could then extradite “fugitive offenders” ad hoc to China and elsewhere. The June 9 demonstrations were largely peaceful, but protesters and police clashed Sunday night and Monday.

Despite the protests, Hong Kong Chief Executive Carrie Lam reiterated her support for the amendment Monday. It’s now scheduled for further debate June 12 in the Legislative Council (LegCo), which is controlled by a pro-Beijing majority.

Why is the topic of extradition so contentious in Hong Kong, a “Special Administrative Region” of China? Here’s a recap of Monkey Cage analysis by political scientists on the amendment itself, as well as the deeper story on rule of law in Hong Kong since the former British colony reverted to Chinese control on June 30, 1997.

1. Why are people in Hong Kong protesting?

Hong Kong legislators actually came to blows over this amendment last month, as Michael C. Davis details in his analysis of the controversial extradition proposal. While Hong Kong has mutual extradition agreements with 20 countries, it has no extradition arrangements with China or Taiwan.

But many in Hong Kong believe the proposed amendment would erode the city’s legal protections and put Hong Kong citizens at risk of extradition to China. “Legal experts speculate Beijing hopes to open the door to extradite corrupt Chinese officials who flee to Hong Kong, as well as perhaps catch local activists in the dragnet,” Davis wrote.

2. Remember the “Umbrella Movement” in Hong Kong? What happened to those protesters?

Sunday’s march wasn’t Hong Kong’s first protest Beijing. In June 1989, thousands rallied against the Tiananmen crackdown. Citizens have gathered for several mass protests against Beijing’s failed promises to uphold the “one country, two systems” model, after the U.K. handed over the city to China in 1997. In 2003, hundreds of thousands of protesters successfully defeated a proposed “national security law” that would have curtailed civil liberties and restricted political groups from working with foreign organizations.

And in 2014, police arrested hundreds of students involved in the “Occupy Central” protests. Protesters, armed with yellow umbrellas to ward off pepper spray from police, blocked Hong Kong’s central commercial area for 79 days. The protest was in response to a “white paper” from Beijing that made clear that only “patriots” would be allowed to run for chief executive in Hong Kong. To many in Hong Kong, this signaled that Beijing intended to keep a tight rein on Hong Kong’s political reforms — and political autonomy.

In April, as Victoria Tin-bor Hui discusses, “a Hong Kong district court convicted nine core leaders of the 2014 Umbrella Movement of conspiracy to commit public nuisance,” handing down prison sentences of up to 16 months. When the “jailed leaders called for a mass demonstration against the extradition law on April 28, 130,000 protesters turned out.”

In an earlier Monkey Cage article, she noted that “In the aftermath of the Umbrella Movement, the Hong Kong government tightened control over universities and high schools, the hotbeds of dissent, by stacking university councils with pro-regime appointees and by introducing patriotic education requirements.”

3. What does “one country, two systems” mean?

All these protests grow from concerns that Hong Kong’s leaders will bow to pressure from Beijing to rein in dissent — and put Hong Kong’s democracy at risk despite promises from the U.K. and Chinese governments to preserve Hong Kong’s autonomy.

As Hui explains, the 1997 handover included “promises of political autonomy guaranteed in the 1984 Sino-British Joint Declaration.” In 1990, finalized in the aftermath of Tiananmen, “Hong Kong’s mini-constitution” — the Basic Law — “was supposed to codify the Joint Declaration’s guarantees of autonomy and the rule of law. Instead, it reflected Beijing’s tighter grip.” The big question now is what happens to core values in Hong Kong — specifically, as Hui notes, “the rule of law, an independent judiciary, free press, impartial police, a neutral civil service.”

This spring’s extradition measure appears to have re-energized the Hong Kong protest movement, bringing out many who had never protested. While the police officially estimated that around 240,000 marched Sunday, other estimates suggest that one in seven Hong Kong residents turned out, with some reportedly waiting hours to march.

Editor’s update: a previous version misstated the date of the Sino-British Joint Declaration. We regret the error.