HONG KONG (Bloomberg) - US President-elect Donald Trump has upped the ante with Beijing by saying he'll use the "one China" policy as a bargaining chip to get a better trade deal.
The policy - the idea that China and Taiwan are part of the same country - has guided US behaviour for decades. China's Communist Party sees Taiwan as a province and its sovereignty as a core interest, so Mr Trump's comments sparked an immediate rebuke.
Here's a look at the policy:
1. What is the "one China" policy?
It is the product of an unresolved civil war between the Kuomintang (KMT) and the Communist Party, in which both claimed to be the rightful government for all of China, including Taiwan. The KMT never gave up that claim despite moving their Republic of China government to Taipei in 1949 after losing a civil war with the Communists, and the idea is enshrined in the island's constitution.
Beijing have made "one China" a prerequisite for countries which want to establish diplomatic relations with Beijing. It has pledged to return to block Taiwan's independence by all means necessary, including war.
2. What did the US agree to?
Through its one-China policy and follow-up pacts, the US acknowledges Taiwan and China are part of the same China, and Beijing is the seat of government.
The US recognised Taiwan from 1913 until the end of 1978. The position began to change under the Nixon administration, with Secretary of State Henry Kissinger negotiating what has become the one-China policy.
The US officially recognised Beijing's government in 1979. Still, a law passed that year by Congress obligates the US to defend peace across the Taiwan Strait and facilitate arms sales to Taiwan.
3. How many countries recognise Taiwan?
The US shift on China prompted an avalanche of countries to follow suit, including some of the world's major powers. Now only 22 smaller nations recognise Taiwan. China seeks greater contact with some of the countries, including Panama and the Vatican, and Taiwan has suggested they may be under pressure from Beijing.
The United Nations only recognises one government - the one in Beijing.
4. Taiwan's parties take different views on the matter?
The KMT, which has ruled Taiwan for most of the last 67 years, sees the mainland and Taiwan as part of the same China while disagreeing with Beijing on what it means - a position known as the 1992 Consensus.
The party's President Ma Ying-jeou, who governed the island from 2008 until May this year, enthusiastically supported this position, leading to warmer ties that culminated in a summit with Chinese President Xi Jinping last year in Singapore.
The Democratic Progressive Party, on the other hand, was founded in 1986 on the idea Taiwan is independent. Ties with Beijing have chilled since Ms Tsai Ing-wen, the DPP leader, succeeded Mr Ma in May and refused to endorse the 1992 consensus.
Even so, Tsai has pledged to uphold the "status quo" and hasn't taken steps towards formal independence.
5. How has calm under the policy helped economic ties?
In 1980, China accounted for 1 per cent of total US trade. By 2015, the mainland accounted for 17 per cent, growing 125 times to US$627 billion in that time. Under a Trump administration, the world may see just how much Beijing's leaders value the one-China policy over those commercial ties.
Foreign Ministry spokesman Geng Shuang told reporters in Beijing on Monday that adherence to the One-China policy was the "political bedrock" for ties.
"If it is compromised or disrupted, the sound and steady growth of the China-US relationship as well as bilateral cooperation in major fields would be out of the question," he said.
China also has economic levers it can pull across the Taiwan Strait on trade and investment. Two-way trade was US$188.6 billion in 2015, according to data from China's customs agency.