When US president-elect Donald Trump spoke on the phone to Taiwan's President Tsai Ing-wen he was going against the long-standing One China policy instituted in 1979.
In that year Washington, under president Jimmy Carter, cut formal diplomatic relations with Taiwan switching recognition to Beijing as the sole representative of China, and no US president or president-elect is believed to have spoken to a Taiwanese leader since then.
Bitter history
The deep rift between China 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 KMT control.
From there, Chiang continued to claim the entirety of China - just as the mainland claimed Taiwan.
Taiwan's full name remains the Republic of China, while the mainland is the People's Republic of China.
Both sides still formally claim to represent all of China.
'One China' policy
In 1992, Taiwan and mainland China both agreed that there is only "one China," covering both places, but they agreed to disagree about what that precisely meant.
The policy means that, essentially, countries must choose which territory represents "one China."
Most countries have chosen Beijing, while also maintaining some ties, if nominally unofficial, to Taipei.
Washington does not formally recognise Taipei, and officially sticks to a the one-China policy that says Beijing is the legitimate government of all of China.
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But in practice, the small island enjoys many of the trappings of a full diplomatic relationship with the United States.
While there is no US embassy in Taipei, Washington runs a nonprofit center called the American Institute in Taiwan, which serves as something of an unofficial consulate.
Many people in Taiwan today remain distrustful of Beijing while others are keen to explore warmer relations, especially when it comes to trade opportunities.
Why the fuss?
The United States has maintained an ambiguous and at times contradictory approach to Taiwan.
On the one hand, America sells high-end weaponry to Taiwan, but it does not formally recognise Ms Tsai, the country's president, as a sovereign leader.
The policy is designed to provide democratic Taiwan with enough military clout to fend off China's vastly bigger armed forces and preserve peace in the region.
Many observers saw the phone call, initiated by Ms Tsai, as a possible shift in long-standing US policy.
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China regards self-ruling Taiwan as part of its own territory awaiting reunification under Beijing's rule, and any US move implying support for independence - even calling Ms Tsai "president," as Trump did in a tweet announcing the call - prompts grave offense in China.
It is also possible that MR Trump, a political novice and a newcomer to the international stage, didn't appreciate the ramifications of the call.
But The Washington Post, citing people involved in planning the call, said it was a deliberate move by the president-elect to strike a new tone, and was months in the making.
Trump says US not necessarily bound by 'one China' policy
Mr Trump said the US did not necessarily have to stick to its long-standing position that Taiwan is part of "one China," questioning nearly four decades of policy in a move likely to antagonise Beijing.
The president-elect's comments on Fox News Sunday came after he prompted a diplomatic protest from China over his decision to accept a telephone call on December 2 from Taiwan's president.
"I fully understand the 'one China' policy, but I don't know why we have to be bound by a 'one China' policy unless we make a deal with China having to do with other things, including trade," he told Fox News.
Chinese officials had no immediate reaction to Trump's remarks.
After Mr Trump's phone conversation with Taiwan's president, the Obama administration said senior White House aides had spoken with Chinese officials to insist that Washington’s “one China” policy remained intact.
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The administration also warned that progress made in the US relationship with China could be undermined by a “flaring up” of the Taiwan issue.
Following MR Trump's latest comments, a White House aide said the Obama administration had no reaction beyond its previously stated policy positions.
In the Fox interview, Mr Trump criticised China over its currency policies, its activities in the South China Sea and its stance toward North Korea. He said it was not up to Beijing to decide whether he should take a call from Taiwan's leader.
"I don't want China dictating to me and this was a call put in to me," he said. "It was a very nice call. Short. And why should some other nation be able to say I can't take a call?"
"I think it actually would've been very disrespectful, to be honest with you, not taking it."
