When the Communists won power on the mainland in 1949 their defeated Nationalist foes retreated to the island of Taiwan, either to go down in a last stand or to "recover the mainland." The Communists, for their part, determined to "liberate Taiwan."
Both sides considered the standoff to be part of a continued civil war. Both claimed legitimate rule over all of China, with Taiwan merely a province of China. The one thing both agreed on was that Taiwan was inextricably part of China, and was not and could not be an independent country.
Until the late 1980s the Nationalists ruled Taiwan as a police state. Danger of communist subversion served to rationalize the dictatorship, although in practice the repression was directed at least as much against agitation for Taiwan independence.
Since the 1980s the island has evolved into a liberal democracy. Advocacy of independence, once considered treason, has become an acceptable political stance. Since 2000, the Nationalist party has alternated in the presidency with the Democratic Progressive Party, whose program in principle calls for independence.
The Nationalists remain in principle open to eventual unification, but not with the crowd currently running Beijing. The actual China policy of the two differs only at the margin: The Nationalists will not actively push for unification and the DPP, given the credible threat of an invasion by the mainland, will not actively push for independence.
Identifying as 'Taiwanese'
In the meantime, as the generations pass, fewer and fewer on the island think of themselves as "Chinese," but identify as "Taiwanese." The island is Chinese in ethnicity and culture, but this need not imply it is properly subject to any Chinese state.
Taiwan remains in limbo: it has all the traits of an independent country, but given China's attitude, the international community is not allowed to say so.
The Beijing authorities no longer talk of "liberation," and say that unification would mean no change in the island's way of life: Taiwan would keep its own political and economic system, even its own armed forces. No mainland soldiers or officials would be sent to the island. For better or worse, these blandishments are not taken seriously by the island's population.
Beijing also allows Taiwan a certain "international space." It can participate in all international fora except those whose criteria include state sovereignty. Other countries can maintain informal relations with Taiwan, and Taiwan with other countries. The various representatives enjoy full diplomatic privileges and immunities, but are not formally accorded diplomatic status.
The United States maintained formal diplomatic relations with the Taiwan regime until 1978. But when America began cultivating a relationship with the People's Republic in the early 1970s, it felt compelled to comply outwardly with the Chinese definition of the situation. So America, too, now has only a nominally informal relationship with Taiwan, with heretofore strict restrictions on what is permitted and what is not. Definitely out has been any kind of direct communication between the two heads of state.
Hence the breach of protocol. To add to the offense, Mr. Trump in his tweet called Ms. Tsai the President of Taiwan, a term anathema to Beijing (more acceptable are "leader of the Taiwan authorities" or "so-called 'President' of the so-called 'Republic of China'").
Curiously, this may reflect continuity with an evolving Obama-era policy. The full historical context of the China-America relationship is not part of the living memory of current American functionaries, and they have been less inclined pre-emptively to humor Chinese whims as one might avoid the temper tantrums of a spoiled child.
How independent is Taiwan?
For, after all, Taiwan is to all appearances an independent state -- one, indeed, as Mr. Trump points out with his characteristic hyperbole, that buys "billions of dollars" of weapons from us, and one that, even in its police state days, has behaved in an exemplary fashion in the international community, and does not deserve the indignity with which it has been treated.
Alas, there are dangers. The current Chinese leadership is certainly not inclined to take military action against Taiwan, as long as Taiwan does not make any explicit moves toward formal independence. But if Taiwan should, China's leaders have talked themselves into a corner: it will be politically impossible for them not to act.
If a Trump administration directly or tacitly encourages President Tsai to push her luck, China may feel compelled to attack. This itself would be tragic, and since Taiwan cannot defend itself without American support, America would be faced with the choice of ignominious abandonment of a friend it had encouraged or a bloody, possibly losing war with China.
Back in the day, critics caricatured the old American policy as "pretending" Taiwan was China and that the mainland "did not exist." This was not accurate, but it was also not without point. It is in principle and logic as fatuous now to pretend that Taiwan as an independent entity does not exist. We can only hope that everyone involved will act carefully.