Frank Ching is a Hong Kong-based journalist.

In Asia – specifically, in the Taiwan Strait, where developments in China, Taiwan and the United States are converging – the political atmosphere is heating up.

Chinese President Xi Jinping is becoming visibly impatient, asserting that unification of Taiwan with the mainland cannot be kicked down the road indefinitely. Taiwan is mired in a presidential election campaign where a leading candidate is likely to press for the highly sensitive proposal to permanently separate the island from China. And in Washington, President Donald Trump is treating China as a strategic threat, and may use Taiwan to provoke the mainland – possibly without realizing the consequences.

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But this knotty crisis is nothing new to those who understand the history of U.S.-China-Taiwan relations.

In the 1940s, the Chinese Communists and Nationalists fought a civil war, which the Communists won. Mao Zedong, the communist leader, proclaimed the establishment of the People’s Republic of China on Oct. 1, 1949, while his Kuomintang (KMT) counterpart, Generalissimo Chiang Kai-shek, fled to the island of Taiwan – a Japanese colony from 1895 to 1945 – and declared Taipei as the capital of his government, the Republic of China.

This is why there are, formally, still two governments that describe themselves as Chinese: one on the communist mainland, which is recognized by most countries, and one in Taipei, which increasingly is being referred to simply as Taiwan, even by the handful of governments that still recognize it.

Forty years ago, on Jan. 1, 1979, when the United States severed diplomatic relations with Taipei to establish them with Beijing, China issued an emotional “message to Taiwan compatriots” calling for reunification. By that time, both Mao and Chiang had died, and the new Chinese leadership headed by Deng Xiaoping made the mainland’s reunification – with British-held Hong Kong and Portuguese-governed Macau, in addition to Taiwan – one of the country’s top priorities.

Though rebuffed by Taiwan, Mr. Deng persisted. In 1982, he unveiled a new Chinese constitution, including a provision on “special administrative regions” to pave the way for the policy of “one country, two systems.”

At that time, there was no democracy in either the mainland or Taiwan. Each was governed by a one-party dictatorship: the KMT in Taiwan and the Communist Party on the mainland.

By 1997, with Britain’s sovereignty over Hong Kong running out as laid out in the Sino-British Joint Declaration, Mr. Deng decided to implement “one country, two systems” in Hong Kong first, so that Taiwan could see how well it worked. And Hong Kong actually became slightly more democratic, with its legislators now elected in one way or another, unlike in colonial times. Currently, 40 of 70 legislators are directly elected while the rest are chosen through narrowly based functional constituencies.

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In Taiwan, however, there has been a political earthquake. In 1996, the year before the Hong Kong handover, Taiwan held its first direct presidential election, with Lee Teng-hui voted in by an island-wide electorate. Previous presidents were chosen by an election committee, which is how Hong Kong’s leader is now chosen; Chief Executive Carrie Lam was picked by a committee of 1,200, most of them pro-China.

Political parties, too, have been maturing in Taiwan. The KMT continued as the ruling party after the introduction of democracy, but in 2000, the opposition Democratic Progressive Party won power, only to lose it after eight years when the KMT regained the presidency. The current president, Tsai Ing-wen, beat her KMT opponent in 2016 and brought about the third transfer of political power in Taiwan.

The genie is out of the bottle. It is not possible now for Taiwan to embrace an election formula akin to that of Hong Kong under “one country, two systems.”

And yet China is acting like nothing has changed in the last 40 years. In January, Mr. Xi gave a major address to recall the “message to Taiwan compatriots” delivered in 1979. He insists that there can be no other way for reunification with Taiwan but “one country, two systems.”

Consistency is an admirable trait in many situations, but not all. There is a well-known quotation, attributed variously to Winston Churchill, John Maynard Keynes and Paul Samuelson: “When the facts change, I change my mind. What do you do, sir?”

When “one country, two systems” was conceived some 40 years ago, it caught the world’s imagination. Now, several decades later, it is proving deeply problematic in Hong Kong and totally inappropriate for Taiwan. If China wants unification, it will have to come up with a new pragmatic and creative solution to suit new circumstances.