US House Speaker Nancy Pelosi's visit to Taiwan has provoked Beijing's ire -- and brought into focus Washington's deliberately ambiguous foreign policy stance toward the democratic, self-ruled island.
Pelosi's pledge Friday that the United States will "not allow" China to isolate Taiwan comes just months after President Joe Biden repeatedly said US forces would defend the island militarily if China attempted to take control of it.
Biden's team have insisted that Washington's decades-old approach remained unchanged.
Here is a recap of that foreign policy stance and why relations between the United States, China and Taiwan are so delicate:
- Bitter history -
The deep rift between Beijing and Taiwan dates back to China's civil war, which erupted in 1927 and pitted forces aligned with the Communist Party of China against the Nationalist Kuomintang (KMT) army.
Eventually defeated by Mao Zedong's communists, KMT chief Chiang Kai-shek fled to Taiwan, which was still under his control.
From there, Chiang continued to claim the entirety of China -- just as the mainland claimed Taiwan as part of its territory to be re-taken one day, by force if necessary.
For years, both sides still formally claimed to represent all of China, and Taiwan's official name remains the Republic of China, while the mainland is the People's Republic of China
Since the late 1990s, Taiwan has transformed from an autocracy into a vibrant democracy and a distinct Taiwanese identity has emerged.
The current ruling party, led by President Tsai Ing-wen, has pledged to defend Taiwan's sovereignty.
Washington cut formal diplomatic relations with Taiwan in 1979, switching recognition to Beijing as the sole representative of China, with the mainland becoming a major trading partner.
But at the same time, the United States maintained a decisive, if at times delicate, role in supporting Taiwan.
Under a law passed by Congress, the United States is required to sell Taiwan military supplies to ensure its self-defense against Beijing's vastly larger armed forces.
But it has maintained "strategic ambiguity" on whether it would actually intervene militarily, a policy designed both to ward off a Chinese invasion and discourage Taiwan from ever formally declaring independence.
There is now growing bipartisan discussion in Washington over whether a switch to "strategic clarity" is preferable given Beijing's increasingly bellicose approach to cross-strait relations.
Beijing has become much more assertive towards Taiwan under President Xi Jinping and the last two years in particular have seen a surge in incursions into Taiwan's air defense identification zone by Chinese military aircraft.
And Russia's war on Ukraine has heightened fears that China might one day follow through on threats to annex its smaller neighbor.
On Friday, China encircled the island with a series of huge military drills, prompting rebuke from Taipei, the United States and other democracies.
Yet analysts broadly agree that despite all its aggressive posturing, Beijing does not want an active military conflict against the United States and its allies over Taiwan -- just yet.
-'One China' policy -
US policy on Taiwan has always hinged on diplomatic nuance.
In what is termed the "One China policy", Washington recognizes Beijing, but only acknowledges the Chinese position that Taiwan is part of China.
It leaves it to the two sides to work out a solution, while opposing any use of force to change the status quo.
In practice, Taiwan enjoys many of the trappings of a full diplomatic relations with the United States.
While there is no US embassy in Taipei, Washington runs a centre called the American Institute in Taiwan.
In the United States, the island's diplomats enjoy the status of other nations' personnel.
Only 13 nations, all in the developing world, and the Vatican still recognize Taiwan.
Beijing has tried hard to stop any international recognition of the island.
It baulks at any use of the word Taiwan, such as when Lithuania allowed Taipei to open a de facto embassy under its own name last year, lest it might lend the island a sense of legitimacy on the global stage.
The United States and a growing number of countries have pushed for Taiwan to be included in UN bodies, such as the World Health Organization.