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What you need to know about Pelosi's visit to Taiwan

Hong Kong/Beijing/Taipei(CNN) US House Speaker Nancy Pelosi landed in Taiwan Tuesday evening, marking a significant show of support for Taiwan despite China's threats of retaliation over the visit.

Pelosi's stop in Taipei is the first time that a US House speaker has visited Taiwan in 25 years. Her trip comes at a low point in US-China relations and despite warnings from the Biden administration against a stop in Taiwan.

The California Democrat is leading a congressional delegation on a tour in Asia this week, which includes stops in Singapore, Malaysia, South Korea, and Japan. Although not included in her official itinerary, expectations that she was planning a visit to Taiwan have fueled US-China tensions since reports of her trip emerged last month.

In a statement after landing, Pelosi and the congressional delegation that accompanied her said the visit "honors America's unwavering commitment to supporting Taiwan's vibrant democracy."

Pelosi, a forthright critic of Beijing, has previously said it is important for the US to show support for Taiwan.

China has lashed out at the visit. In a statement following Pelosi's arrival, China's Foreign Ministry said the trip would have a "severe impact on the political foundation of China-US relations."

"China will definitely take all necessary measures to resolutely safeguard its sovereignty and territorial integrity in response to the US Speaker's visit," the statement said.

A spokesman for China's Ministry of Defense said the People's Liberation Army was "on high alert" and would launch "a series of targeted military operations to counteract the situation, resolutely defend national sovereignty and territorial integrity, and resolutely thwart the interference of external forces and 'Taiwan independence' secessionist schemes."

Prior to the visit, US officials had been worried that China could respond militarily, potentially triggering the worst cross-strait crisis in decades. Last week, China's Defense Ministry warned: "If the US insists on taking its own course, the Chinese military will never sit idly by."

The tensions provided the backdrop for a lengthy phone call between US President Joe Biden and Chinese leader Xi Jinping on Thursday, in which Xi warned the US not to "play with fire" on the Taiwan issue. Neither side immediately confirmed if Pelosi's reported plans were discussed, though a US official later confirmed they were. Preparation for the call predated reports of the trip.

Here's what you need to know about the high-stakes visit.

Why is Beijing angry about Pelosi's visit?

China's ruling Communist Party claims the self-ruled democracy of Taiwan as its own territory -- despite never having governed it -- and has not ruled out the use of force to "reunify" the island with the Chinese mainland.

For decades, Beijing has sought to isolate Taipei on the world stage, from chipping away at its diplomatic allies to blocking it from joining international organizations.

Any move that appears to lend Taiwan a sense of international legitimacy is strongly opposed by China. And in the eyes of Beijing, high-profile overseas visits by Taiwanese officials, or visits by foreign officials to Taiwan, will do just that.

In 1995, a visit by Taiwan's then-President Lee Teng-hui to the United States triggered a major crisis in the Taiwan Strait. Enraged by the trip, China fired missiles into waters around Taiwan, and the crisis ended only after the US sent two aircraft carrier battle groups to the area in a forceful show of support for Taipei.

In recent years, Taiwan has received a flurry of visits by US delegations, consisting of sitting and retired officials and lawmakers. That has drawn angry responses from China, including sending warplanes into Taiwan's self-declared air defense identification zone.

But Pelosi's political stature makes her visit all the more provocative to Beijing.

"Pelosi is the third public official in the line of succession after the President and Vice President, I think the Chinese take that very seriously," said Susan L. Shirk, chair of the 21st Century China Center at UC San Diego.

"So she is a very important figure in American politics. It's different from your ordinary member of Congress."

Pelosi is a longstanding critic of the Chinese Communist Party. She has denounced Beijing's human rights record, and met with pro-democracy dissidents and the Dalai Lama -- the exiled Tibetan spiritual leader who remains a thorn in the side of the Chinese government.

In 1991, Pelosi unfurled a banner in Beijing's Tiananmen Square to commemorate victims of the 1989 massacre of pro-democracy protesters. More recently, she has voiced support for the 2019 pro-democracy protests in Hong Kong.

Why is the trip fueling US-China tensions?

Beijing sees Pelosi's trip as a "serious violation" of historical US-China agreements governing their relations.

The US formally switched diplomatic recognition from Taipei to Beijing in 1979 -- but has long trod a delicate middle path. Washington recognizes the People's Republic of China as the sole legitimate government of China, but maintains close unofficial ties with Taiwan.

The US also supplies Taiwan with defensive weaponry under the terms of the decades-old Taiwan Relations Act, but it remains deliberately vague on whether it would defend Taiwan in the event of a Chinese invasion -- a policy known as "strategic ambiguity."

China's authoritarian turn under Xi's leadership and plummeting relations with Washington have pulled Taiwan closer into the orbit of the US. This has infuriated Beijing, which has accused Washington of "playing the Taiwan card" to contain China's rise.

The US, meanwhile, has stepped up its engagement with Taiwan, approving arms sales and sending delegations to the island.

Since the Taiwan Travel Act was signed into law by then-US President Donald Trump in March 2018, US officials and lawmakers have embarked on more than 20 trips to the island, according to a CNN tally. The 2018 law encourages visits between officials of the US and Taiwan at all levels.

Taiwan figured prominently in Xi and Biden's two-hour-and-17-minute phone call, with the Chinese leader urging Washington to honor existing agreements with Beijing both "in word and in deed," according to a readout from China's Foreign Ministry. The statement added that China would "resolutely safeguard" its national sovereignty.

For his part, Biden reiterated that US policy "had not changed," according to a White House readout of the call.

"The United States strongly opposes unilateral efforts to change the status quo or undermine peace and stability across the Taiwan Strait," Biden said, according to the statement.

Has a US House speaker ever visited Taiwan?

Pelosi's trip isn't the first time a sitting US House speaker has visited Taiwan.

In 1997, Newt Gingrich visited Taipei only days after his trip to Beijing and Shanghai. China's Foreign Ministry criticized Gingrich after his Taiwan visit, but the response was limited to rhetoric.

Former US House Speaker Newt Gingrich meets with Taiwanese Vice President and Premier Lien Chan during a brief visit to Taiwan in April, 1997.

But twenty-five years on, China is stronger, more powerful and confident, and its leader Xi has made it clear that Beijing will no longer tolerate any perceived slights or challenge to its interests.

"China is in a position to be more assertive, to impose costs and consequences to countries that don't take China's interest into consideration in their policymaking or actions," said Drew Thompson, a visiting senior research fellow at the Lee Kuan Yew School of Public Policy at the National University of Singapore.

But the decision not to include Taiwan on the official itinerary released by the delegation "preserves the unofficial nature of the visit," and should be a "good outcome for Beijing and US-China relations," Thompson added on Twitter following the release of Pelosi's statement Sunday listing her itinerary.

What about the timing?

Pelosi's visit comes at a sensitive time for China.

The House speaker had previously planned to lead a US congressional delegation to Taiwan in April, but postponed the trip after she tested positive for Covid-19.

The Chinese military celebrated its founding anniversary on August 1, while Xi, the country's most powerful leader in decades, is preparing to break conventions and seek a third term at the Communist Party's 20th congress this fall.

In August, Chinese leaders are also expected to gather in the seaside resort of Beidaihe for their annual summer conclave, where they discuss personnel moves and policy ideas behind closed doors.

"It's a very tense time in Chinese domestic politics," Shirk said. "(Xi) himself and many other members of the elite in China would view the Pelosi visit as a humiliation of Xi Jinping (and) his leadership. And that means that he will feel compelled to react in a way to demonstrate his strength."

While the politically sensitive timing could trigger a stronger response from Beijing, some experts believe it could also mean the Communist Party would want to ensure stability and prevent things from getting out of control.

"Honestly, this isn't a good time for Xi Jinping to provoke a military conflict right before the 20th party congress. It's in Xi Jinping's interest to manage this rationally and not instigate a crisis on top of all the other crises he has to deal with," Thompson said, citing China's slowing economy, deepening real estate crisis, rising unemployment, and constant struggle to curb sporadic outbreaks under its zero-Covid policy.

How has China reacted?

China's military will start exercises around Taiwan in response to US House Speaker Nancy Pelosi's visit to the self-governed island and launch a series of "targeted military operations to counteract the situation," according to statements released by its Eastern Theater Command and Ministry of Defense Tuesday.

"Starting from the evening of August 2, the Eastern Theater Command will carry out a series of joint military operations around Taiwan Island, and conduct joint air and sea exercises in the sea and air spaces of the northern, southwestern and south-eastern Taiwan Island, conduct long-range live ammunition firing in the Taiwan Strait, and organize regular-guided-fire testing in the eastern waters of Taiwan Island," Col. Shi Yi, spokesman for the Eastern Theater Command, said.

"This action is a solemn deterrent against the recent major escalation of the negative actions of the United States on the Taiwan issue, and a serious warning to 'Taiwan independence' forces," the statement added.

The Eastern Theater is one of the five joint commands of the People's Liberation Army with jurisdiction over China's eastern coastal provinces of Fujian and Zhejiang, which sit opposite and above Taiwan.

Prior to her arrival, national security officials quietly worked to convince Pelosi of the risks her trip to Taiwan could pose, while the Pentagon developed a security plan to use ships and aircraft to keep her safe.

The constant worry among US officials is that miscalculations or inadvertent incidents or accidents could occur if China and the US significantly increase their air and maritime operations in the region.

But US does not expect direct hostile action from Beijing during a visit by Pelosi. At least five defense officials, speaking prior to her arrival, described this as a very remote possibility and said the Pentagon wants to see the public rhetoric lowered.

What has Taiwan said about Pelosi's trip?

Pelosi was welcomed at the airport by Taiwan Foreign Minister Joseph Wu, and the iconic Taipei 101 skyscraper was lit up with a welcome message for the speaker praising "US-Taiwan friendship forever."

Taiwan's President Tsai Ing-wen will receive Pelosi and her delegation at the Presidential Palace on the morning of August 3, according to a statement from the president's office.

Presidential Spokesperson Xavier Chang said that Speaker Pelosi had not only supported Taiwan for a long time, but also paid attention to Taiwan's democratic development and regional peace and security.

But prior to her arrival, Taiwan had been tight-lipped about the situation. When Pelosi's visit was first reported by the Financial Times last week, Taiwan's Ministry of Foreign Affairs said it had "received no information" about the visit.

During a regular news briefing on Thursday, a ministry spokeswoman reiterated it had not received any definite information on whether Pelosi would be visiting the island and had "no further comment" on the matter.

"Inviting members of the US Congress to visit Taiwan has long been a focus of the Ministry of Foreign Affairs of Taiwan and our Taipei Economic and Cultural Representative Office in the United States," spokeswoman Joanne Ou said.

Though international media is closely watching events, the escalating tension barely made headline news in Taiwan this week. Taiwan's media has mostly focused on upcoming local elections and Taiwanese military drills.

Previously, Taiwanese officials have publicly welcomed visits by US delegations, seeing them as a sign of support from Washington.

CNN's Kylie Atwood in Washington, DC, contributed to this report.