There’s a reason Donald Trump’s impetuous conversation with Taiwanese President Tsai Ing-wen has left foreign-policy experts tearing their hair out by the roots. The fussy diplomatic protocols Trump flouted, in this case, are not a mere formality. They are a finely honed coping strategy for Chinese emotions that are very raw and potentially explosive. Although the Chinese reaction has been surprisingly — perhaps hopefully — muted, there is no more sincerely sensitive issue in China, among politicians and the public, than Taiwan.

Taiwan, or the Republic of China, was founded by the fleeing Kuomintang (KMT or “Nationalist Party”), the modernizing but corrupt, authoritarian and incompetent rulers of China in the 1930s, after they lost the mainland to the Communist Party, the modernizing but corrupt, authoritarian and incompetent rulers of China from 1949 to the present. They fled to the conveniently defensible island on China’s southern margins, once famous as a haven for pirates and later a Japanese colony.

The republic still claims to be the legitimate successor to the Chinese state, as does — with considerably more force behind it nowadays — Beijing. Both are publicly committed to the idea of a single China; they merely disagree vehemently about which one it is. (That’s the public position, anyway; millions of Taiwanese, especially the young, are willing to acknowledge the possibility of full independence.) In the past, Taiwan was even more revanchist about the borders of China than Beijing; it refused to acknowledge the existence of Mongolia until 2002 — 91 years after Mongolia broke away from the flailing corpse of the Manchu-ruled Qing dynasty that also controlled China.

The whole thing is a giant mess of political fictions and competing histories. China’s historical claim to the island is far sketchier than its own propaganda makes out, as with vast stretches of the country’s border regions elsewhere; its argument that a democratic state should surrender its sovereignty to a distant and unloved tyranny is deeply unconvincing. A forcible invasion would be a publicity disaster for China and maybe also a military one; its plan has always been to push for long-term political reconciliation, which seemed to be on course until the upstart Democratic Progressive Party in Taiwan disturbed the comfortable relationship that the Chinese Communist Party and KMT had developed in recent years. But that doesn’t make the divide any less painful or the feelings of most Chinese any less real.

In China, it’s not an avoidable issue. When I worked in English-language Chinese state media, the importance of using the “correct” vocabulary for Taiwan was hammered into staff on a regular basis. The reasoning behind some decisions about the correct form, made decades ago, was opaque; “mainland China” was verboten, for instance, but “the Chinese mainland” was fine, and it was the “Taiwan question,” not the “Taiwan issue.” It was more obvious why Taiwan couldn’t have a president, although “leader” was acceptable.

A little before I arrived at one newspaper, there had been a small witch hunt to find who was responsible for this sentence: “The paper factory is the largest in China and the second-largest in the world.” After two days of investigations, the guilty Chinese reporter was fined about a third of her monthly salary, had to write a self-criticism letter, and strict protocols were put in place to make sure such a disaster was avoided in the future. Why the problem? The largest paper factory was in Taiwan, and so the sentence — copied unthinkingly from a foreign source that didn’t suffer from such sensibilities — was dangerously splittist.

In moments of particular stress, “Taiwanese” was forbidden, the adjectival form believed to imply unacceptable separatism. I would strenuously point out that “Californian” implied no allegiance to the Bear Flag Republic and that our many references to Sichuanese, Henanese and Yunnanese had not yet meant a return to the Warring States, and eventually sanity would usually prevail.

Like a puritan’s sexual fears, the obsession with belittling Taiwan’s status actually ends up drawing constant attention to it. Sentences such as “Taiwan’s so-called ‘president,’ Tsai Ing-wen, addressed the so-called ‘legislature’ of the Chinese island of Chinese Taiwan, a province of China, yesterday” regularly deface articles in Chinese newspapers. The fixation isn’t limited to the media. Chinese customs confiscates globes and atlases that have the effrontery to show Taiwan in a different color from the mainland. Chinese education officials tear Taiwanese adverts out of conference booklets. Chinese students throw hissy fits at Taiwan being listed as a country at Model U.N. events.

And there’s the real problem. This isn’t just a set of political restrictions imposed by a paranoid party — one that has always been obsessed with controlling and contorting language. It’s bone-deep in mainland Chinese, a conviction drummed into them by childhood and constantly reasserted. Plenty of elements of party propaganda are inconsequential to most Chinese or even mocked. Taiwan isn’t one of them.

I have lived in China for 13 years, and in that time I have talked with perhaps three mainlanders who thought that Taiwan had the right to determine its own future. Everyone else with whom I’ve discussed the issue, from ardent liberals to hardcore Marxists to the politically apathetic, has been fervently against the idea that Taiwan could ever be considered a country. It’s an idea as weird, taboo and offensive to the majority of Chinese as proposing the restitution of slavery would be to Americans — not for its moral value but for going against everything they hold dear about their country.

Most of the time, when Beijing says something has “hurt the feelings of 1.3 billion Chinese,” it’s petulant bull; on Taiwanese issues it comes closer to the truth. On the WeChat Moments feed of a former student, a bright and intellectually curious teenager, I saw her rage at finding the Taiwanese flag on the wall of a dorm at her new American university. “IT’S NOT A COUNTRY!” she indignantly declared, her anger echoed by her (Chinese) schoolmates follow-up comments.

This is, of course, a deeply unthinking attitude. It’s a product of decades of propaganda about China’s (real but century-old) humiliations at the hands of foreign powers. It arises, too, from a complex of neuroticisms and resentments about Taiwan’s wealth and success in the past, now mixed with smugness at the mainland’s new power. And for ordinary Chinese, it’s a result of the constant lessons — beginning with kindergarten rhymes and reinforced every week by their parents, peers and teachers — about China’s supposed oneness and the evil of those who would split the country.

It’s an unhappy and bitter part of Chinese nationalism, one that denies both the six-decade reality on the ground and the agency of Taiwanese to decide their own future. But it’s not going to disappear overnight. If the Communist Party vanished into smoke tomorrow, Chinese would still be contemptuous of Taiwanese aspirations and furious with anyone who suggested otherwise.

On America’s part, the issue needs to be handled carefully, respectfully and with a certain allegiance to diplomatic fictions. Anything else risks stirring not just Beijing’s ire but genuine public anger — a force that Beijing itself might sometimes manipulate but may also not be able to entirely control.