Al-Huriya News Agency - President-elect Donald Trump had a 10-minute phone conversation with Taiwan's president Tsai Ing-wen on Friday.

It's not unusual for the incoming leader of one government to have a chat with the sitting leader of another, if only to exchange pleasantries, but Trump's call with Tsai is causing a huge diplomatic storm.
A lot of speculation is swirling around about what it means for the future of U.S. relations with China and Beijing's relations with Taipei. Here's why:

1. Who's the boss?

China and Taiwan both agree there is only one nation of China. But the jury is still out on who the legitimate ruler actually is. It has been this way since 1949 after the communists won the civil war and forced the nationalists, who previously ruled, to flee the mainland to the island of Taiwan. The communists set up a new government with the capital in Beijing, officially proclaiming the birth of the People's Republic of China (PRC). The nationalists set up their own government in Taiwan still officially known as the Republic of China (ROC). In practice, the PRC governs most of the Chinese territory and the ROC governs Taiwan and a few smaller islands near it. Most countries recognize the PRC as the legal ruler of all of China.
2. Renegade province
Despite having separate governments, China claims Taiwan is a renegade province. Taiwan runs itself like a country, having its own ministries and national and foreign policies separate from China. It even has formal diplomatic ties with 21 countries that officially recognize the ROC. But the ROC does not have nation status at the United Nations and most other international bodies.
3. One-China Policy
U.S. relations with China and Taiwan are governed by a set of protocols known as the One China Policy. In 1979, the US acknowledged the PRC's claim that there is one China and that Taiwan is part of China, when Washington severed ties with Taipei to recognize Beijing . The U.S. maintains unofficial ties with Taiwan and posted "unofficial" representatives to Taipei. Until now, there have been no formal visits or official conversations between a U.S. president or president-elect and Taiwan's leaders. When Trump took Tsai's call, he broke this sensitive protocol.
4. The political elephant in the room
The threat of a military conflict between China and Taiwan remains constant, for decades there were no communications, travel or trade between the two countries. Tensions began to ease in the 1990s when Beijing and Taipei reached an agreement to allow deliberate ambiguity on questions of sovereignty. This paved the way for economic and cultural cooperation. Since then, Taiwanese businesses have invested billions into the mainland and millions of Chinese tourists have visited Taiwan since the resumption of direct flights.
5. China views Tsai's party warily
China fears, rightly or wrongly, that Tsai Ing-wen's Democratic Progress Party, is committed to declaring formal independence for Taiwan. The "I" word is something that China will never accept. Beijing insists Taiwan must be reunited with the mainland -- by force if necessary. Although Tsai has said she wants to preserve the status quo and not make any moves towards formal independence, her initiating a call to Trump, which the President-elect agreed to take could rub Beijing the wrong way.