China’s ruling Communist Party now presides over the world’s second largest economy and appears to enjoy broad popular support at home. It has been so successful at erasing the 1989 massacre from history that many young Chinese have no idea it happened. So does it still matter? Yes, and here’s why:

This past fall, the People’s Republic of China surpassed the Soviet Union in longevity, celebrating a record 69 years of Communist rule. In an essay at the time, I tried to explain how the party defied the odds. A key piece of the puzzle? The protests in 1989 so frightened the party’s leaders — and the army’s violent response proved so divisive and traumatic — that they resolved never to let anything like it happen again.

For 30 years, that fear has served the party well, like a “vaccination” against “political turmoil,” as one state newspaper put it on Monday. The party took risks it otherwise might not have, embracing economic change to deliver prosperity. And it has been ruthless about coming down hard on people who dare seek greater political freedom.

In Hong Kong, where such freedoms are eroding, tens of thousands will nevertheless participate in a vigil for the massacre victims tonight. There are signs of resistance on the mainland too: An army journalist speaking out after 30 years of silence. A fresh leak of party documents about the crackdown. The publication of long-hidden photos.

Nicholas Kristof, whose coverage of the massacre won the Pulitzer Prize, argues in his column that China’s growing middle class will be more difficult for the party “to fool, bully and bribe into perpetual submission.” But the new middle class also has more to lose, while technology has strengthened the security forces. “The future looks more like 1984,” one of the few prominent figures from the protests still active in China told my colleague Chris Buckley.

There is another reason what happened at Tiananmen still matters. For seven dramatic weeks in the spring of 1989, the world saw the best and worst of China — and it has not forgotten. Now, with Washington moving aggressively to confront Beijing as a trade partner and geopolitical rival, the disputes often boil down to this: Can America trust China? The shadow of the massacre looms over the question, in part because the government has never acknowledged it was wrong.

— Phil Pan