The millions of Hong Kong residents who filled the streets of the island city this month are an inspiration. They achieved what seemed impossible.

Thanks to their courageous protests, they faced down the looming shadow of Chinese President Xi Jinping and forced Carrie Lam, the Beijing-backed Chief Executive of Hong Kong, into retreat on proposed legislation that would have exposed people in Hong Kong to the threat of extradition into the black hole of China’s legal system.

The victory, however, is tenuous. As powerful and moving as the protests have been, Ms. Lam’s apology and retreat are a tactical move. It would be foolish to imagine Beijing won’t renew its push.

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Authoritarian China’s steady encroachment on the Hong Kong Special Administrative Region has been patient and methodical; in the mind of the Chinese government, it is overdue. The “one country, two systems” pact, which took effect in 1997 with Britain’s handover of Hong Kong to China, was first agreed to in 1984, effectively eons ago in the story of modern China.

Beijing and Mr. Xi surely see the end of the 50-year agreement in 2047 as right around the corner. Hong Kong, and the world, must be vigilant. This month’s massive protests are the middle chapter of an epic struggle, not the end.

At issue is a proposed law that would allow Hong Kong citizens to be extradited, on minimal evidence and with only a brief court appearance, to face charges in China. If passed, it would put every one of the territory’s 7.4 million people at risk, including at least 300,000 Canadian citizens. It would jeopardize anyone doing business in or travelling to Hong Kong. That would be bad for the city’s economy, but far worse for human rights and the rule of law. And it would be the most serious erosion yet of Hong Kong’s freedoms at the hands of Beijing.

The threat is clear. In the Chinese legal system, the only true authority is the Communist Party. There is no rule of law. Allowing extradition to China is a way for Beijing to exert its whims in Hong Kong; the party could easily concoct charges against anyone who displeases it and disappear them into one of the country’s prisons.

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Pressure against the extradition law has mounted all spring. In April, more than 100,000 Hong Kong residents marched in the streets. A delegation of Hong Kong democracy and human-rights leaders visited Canada and the United States in early May to rally support. A number of U.S. legislators in late May called for the extradition law to be withdrawn. Canada chimed in, too.

But the real story has been the past 10 days. On June 9, an estimated one million Hong Kong residents marched. Ms. Lam held firm. A second major protest came last Wednesday. Police fought protesters with tear gas and rubber bullets. Official work on the legislation was pushed back. And then, on Saturday, Ms. Lam retreated and suspended the proposals.

Hong Kong citizens are fighting on, though. Upwards of two million were on the streets the next day – more than a quarter of the city’s population. Ms. Lam apologized and has since signalled she will not revisit the proposals during her remaining three years in office.

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The result of the protests is a surprising and buoying outcome, especially when compared with the Umbrella Movement of 2014, when young people took to the streets for 79 days calling for a greater democratic voice, but achieved nothing. Beijing won that round.

This win by Hong Kongers is the first since the ruthless Mr. Xi came to power in 2012. Young people in Hong Kong know no life outside the constant spectre of Chinese rule. The children of 1997 are 22 this year. Their fight is an existential one.

Beijing feels the threat. Its censors have worked to obscure the news of Hong Kong in China. Canada and its allies must therefore keep up their support. U.S. legislators this month threatened to end Hong Kong’s special trading status with the United States if the extradition treaty goes through – a move that, if carried out, would prompt many businesses to decamp to Singapore, among other places.

The Group of 20 convenes next week in Osaka, Japan. Mr. Xi is scheduled to meet with U.S. President Donald Trump. The United States, Canada and the democratic world must speak in a clear voice and honour the people of Hong Kong, who stood up to Beijing and won – for now. The struggle to preserve Hong Kong’s freedoms will only get more difficult.