Taiwan's separate status, says China's leader, Xi Jinping, is "a wound to the Chinese nation left by history." Is a crisis coming? Here's everything you need to know:

What does China want?
China has always considered Taiwan its territory, and reunification is an almost sacred cause. Tensions across the Taiwan Strait have led to conflict or near-conflict at least three times since 1949, and they are ratcheting up again. Chinese leaders have been alarmed since Taiwanese President Tsai Ing-wen of the Democratic Progressive Party was elected in 2016; while she doesn't explicitly call for independence, she has told Beijing it must respect the island nation's sovereignty and the wishes of the Taiwanese people. In a major speech last month, Chinese President Xi Jinping warned that Taiwan would eventually be incorporated, one way or another. "We make no promise to abandon the use of force," he said. "That the two sides of the strait are still not fully unified is a wound to the Chinese nation left by history." Xi said that Taiwan's rights could be protected under the "one country, two systems" approach adopted when Hong Kong was absorbed in 1997. Tsai pointedly responded that Taiwan, a free society with a boisterous democracy, was not interested in being absorbed by the mainland. She said Hong Kong's experience shows that rule from Beijing "leads to a loss of freedom, rule of law, and human rights."

When was Taiwan part of China?
Taiwan, 110 miles from the mainland, was inhabited by Austronesian-speaking aborigines before being annexed by the Qing dynasty in 1683. Japan captured it and ruled it from 1895 to 1945, when Chiang Kai-shek, the Chinese nationalist leader, took it back in the name of the post-imperial Republic of China. In 1949, Chiang's Kuomintang lost China's civil war to Mao Zedong's Communists and fled to Taiwan, which inherited the Republic of China name, while on the mainland Mao declared the People's Republic of China. Each government insisted it represented all of China. Washington took Taiwan's side, seeing it as a bulwark against communism during the Cold War. Taiwan, as the Republic of China, represented China at the United Nations until 1971.

How was Taiwan governed?
For decades, it was authoritarian, just as China is now. Chiang's party, the Kuomintang (KMT), imposed martial law until 1987, imprisoning tens of thousands of dissidents and executing some 4,000. Yet Taiwan also grew rich: Its economy exploded in the 1960s, until by the early 2000s it led the world in production of computer equipment and bicycles. After Chiang died in 1975, Taiwan began to evolve from a one-party state controlled by the KMT into a thriving democracy of 23 million people. It held free elections in 1992, and had its first partisan transition in 2000, when the opposition Democratic Progressive Party took power. Last year, Taiwan increased its use of direct democracy by adopting one of the most citizen-friendly systems for ballot initiatives and referendums in the world.

How are relations with China?
Trade is booming, but diplomatic relations are very tense. The KMT officially favors eventual reunification. The DPP, which is currently in power again, leans toward eventual independence. Taiwanese today have a strong sense of Taiwanese national identity. In a survey last month, 75 percent of Taiwanese said they oppose "one country, two systems." But Beijing continues to insist that there is only "one China," which includes Taiwan.

What is the U.S. role?
Washington no longer has official relations with Taiwan, but that is largely a diplomatic fiction; it is still a major ally. Early in the Korean War, when Mao was threatening to invade Taiwan, President Harry Truman ordered U.S. forces to protect the island, and Washington has implicitly guaranteed its safety ever since. A rift came in 1972, when the U.S. established relations with Beijing and acceded to the Chinese demand that Taiwan surrender its U.N. seat. In 1979, with U.S. businesses eager to get access to the vast Chinese market, President Jimmy Carter agreed to open full diplomatic relations with China, and accepted Beijing's condition that the U.S. officially sever relations with Taiwan. Congress, though, objected to this treatment of a long-term ally and passed the Taiwan Relations Act, which offers a qualified commitment to support Taiwan's self-defense. Since then, the U.S. has supplied vast amounts of weaponry to Taiwan — $15 billion worth over the past decade.

What led to the current tension?
China fears that the U.S. is conspiring with Taiwan on its dream to be truly independent, as part of the growing great-power competition between Beijing and Washington. President Trump angered Beijing right after his election by telephoning President Tsai, a direct communication that overturned four decades of diplomatic practice since the 1979 break in relations. Exacerbating the tension, Congress last year unanimously passed the Taiwan Travel Act, which allows senior officials to visit between Taipei and Washington. In a show of both irritation and force, China has stepped up military drills and sent an aircraft carrier and other vessels through the strait. In response, U.S. warships have patrolled the waters off Taiwan. A new crisis "could be triggered by any of the three parties," says Professor Jie Dalei of Peking University, and would be "a losing proposition for all sides."

Entwined economies
Starting in the early 1980s, China has tried to bring the Taiwanese into its orbit by emphasizing the benefits of economic ties. At that time, Taiwanese companies invested billions in the mainland, becoming important drivers of China's own technological development. Chinese tourists visited Taiwan in the millions, and both countries prospered as China's economy grew. Now, more than 100,000 Taiwanese businesses operate on the mainland. Foxconn, Taiwan's largest employer, has 12 factories in nine Chinese cities, where it makes Apple's iPhones, Amazon's Kindles, and Sony's PlayStations. Some 40 percent of Taiwan's exports go to China. President Tsai, though, is wary of Taiwan's dependency on China, and she is cultivating other markets, such as India. She has vowed to "bid farewell to our past overreliance on a single market," saying it left Taiwan vulnerable to economic blackmail by Beijing.