Pro-democracy activist Joshua Wong is detained by police officers in Golden Bauhinia Square in Hong Kong on Wednesday. (Vincent Yu/Associated Press)

Martin Lee has worked for five decades as a barrister and advocate for Hong Kong and was founding chairman of the Democratic Party of Hong Kong.‎ Joshua Wong is the secretary general and co-founder of Demosisto, a political party in Hong Kong.

Xi Jinping is making his first visit to Hong Kong as president of China, to celebrate the 20th anniversary of the 1997 handover from Britain to China. The central government will insist on fireworks, but the world should know the darkening threats to freedom, the rule of law and free markets in Hong Kong.‎

We are two Hong Kong democracy advocates separated by six decades in age — one of us is 79, the other 20 — united in our conviction that democracy is essential to save Hong Kong’s way of life. We also believe that a democratic future for the territory is in China’s own national interest.

The basis for the transfer of Hong Kong’s sovereignty and people was established by the 1984 Joint Declaration, an international treaty registered at the United Nations. In that treaty, Hong Kong people were promised “one country, two systems,” with “Hong Kong people ruling Hong Kong with a high degree of autonomy.” Our rights, freedoms, rule of law and way of life were supposed to continue for at least 50 years.

A central promise was that we Hong Kong people would in 10 years’ time progress toward elections based on universal suffrage. This arrangement protected free political speech in the city and kept alive hopes for genuine democracy that we were also denied under British rule.

Twenty years later, we are still waiting for the “two systems” to be implemented through genuine universal suffrage, without which we can never be masters of our own house.

The past several years have delivered an acceleration of worrying encroachments, including Beijing’s extrajudicial abductions of five publishers and a businessman from Hong Kong, threats to journalists and media freedom, the removal of elected legislators, a surge in arrests of student activists, and attacks on our independent judiciary. Our clean markets are increasingly tainted by crony corruption from China, and our government is effectively controlled by Beijing’s apparatchiks from the Central Liaison Office in Hong Kong.

The challenges we face were exemplified by the 2014 Umbrella Movement demonstrations, when tens of thousands took to the streets to demand greater democracy — a demand that remains unmet. Our fellow citizens often ask us, “Haven’t you failed?”

To be sure, our long fight hasn’t achieved our stated goals. But looking back at the 20 years since the 1997 handover, there are many reasons for optimism about the future, alongside the need for action to protect basic human rights.

Hong Kong journalists, lawyers, students, religious leaders, teachers, business executives and other citizens have resisted every encroachment by Beijing. We have fought to preserve our core values, including the rule of law, transparency, a free flow of information and free markets — the values that have long been a beacon for China and beyond.

Hong Kong has faced many crises. In the 1980s, our resilient citizens weathered the announcement that Hong Kong would be handed over to China. We mourned Tiananmen Square’s dashing of aspirations for democracy in 1989, and we raced against time to build and entrench Hong Kong’s own political institutions despite opposition from the British and now the Chinese.

For our young people, this long road to democracy in order to preserve the rights we were promised is a reminder that freedom is not free. It takes vigilance and persistence, a battle that sometimes extends across generations.

These young people understand very well what makes Hong Kong special and different from mainland China. They have a life ahead of them based on “two systems.” They don’t want to live in a Hong Kong that becomes ever more like China’s system of cronyism and corruption. They value academic freedom, press freedom and the ability to protest, speak, use social media and write freely.

This young generation has now seen 20 years of the older generation trying and failing to get Beijing to honor its promise of “two systems.” They have more reason than their parents and grandparents not to trust Beijing’s promises. They understand that the assurances of the Basic Law, our mini-constitution, have been broken. They don’t trust the present and won’t wait another 20 years.

Let us be clear: Hong Kong people are not challenging Beijing. We are merely insisting that China uphold its pledge to let us freely choose our leaders by universal suffrage and exercise the “high degree of autonomy” we were promised by China.

Above all, China needs to make sure that Hong Kong’s “two systems” survive in order to give the younger generation an incentive to stay and build on our success. Taiwan also continues to watch to see if Beijing’s word can be trusted.

As Xi spends time in Hong Kong, we hope he personally reverses the dangerous course of the past two decades and affirm that our freedoms and way of life are good for China, too. If Xi wants Hong Kong people to celebrate 20 years of Chinese rule, this is the moment to finally make good on Beijing’s promise of democracy and free and fair elections. ‎He should begin by understanding and trusting Hong Kong — and especially our young people.