US House of Representatives Speaker Nancy Pelosi arrived in Taipei on Tuesday night (Aug 2) in defiance of threats from China.
The visit by Mrs Pelosi is worsening a rift in ties between the United States and China.
It is part of her Asia trip, which started in Singapore on Monday (Aug 1), followed by Malaysia on Tuesday. She is also scheduled to visit South Korea and Japan.
Here's a look at why her visit to Taiwan is raising tensions.
1. The highest-ranking US leader to visit in 25 years
The visit by Mrs Pelosi - second in line to the US presidency after Vice-President Kamala Harris - is the first visit by a US speaker in 25 years since Mr Newt Gingrich visited Taiwan in 1997.
Mrs Pelosi is a Democrat, like President Joe Biden. Mr Gingrich, however, is from the opposing Republican Party and was then House Speaker under Democratic President Bill Clinton's administration. Just before his Taiwan visit, Mr Gingrich had also visited Beijing under more friendly conditions, with then Chinese President Jiang Zemin describing US-China relations as entering a state of "sunshine after the rain" following the visit.
China's ambassador to the United Nations Zhang Jun told reporters on Monday that a visit by Mrs Pelosi is not comparable to Mr Gingrich's, saying that "an early mistake does not make the following mistake legitimate".
Beijing sees any official contact with Taiwan as a recognition of the island's government, even though Washington maintains it has not budged from its "One China" policy of recognising Beijing over Taipei and that Taiwan is a part of China.
2. China's new status as global superpower
At the time of Mr Gingrich's visit to Taiwan in April, 1997, China had other priorities. It was preparing for the British handover of Hong Kong on July 1 that year. The government was also looking to exit its eight-year diplomatic isolation following its 1989 Tiananmen Square crackdown on pro-democracy protests.
More than 25 years later, China - under the leadership of President Xi Jinping - is the world's No. 2 economy, and commands a vastly improved military. It is not willing to compromise over Taiwan which it views as a renegade province it seeks reunification with, but has never renounced the use of force to do so.
The timing of the visit also comes just months before the 20th National Congress of the Communist Party of China, that will reportedly be held in November. Mr Xi is widely expected to seek an unprecedented third term as president. The reunification of Taiwan is a key goal of Mr Xi's administration.
3. Pelosi showmanship worsening frosty US-China ties
The US under the Biden administration has been increasingly at odds with China. For example, it has frequently questioned Beijing's stance over Russia's invasion of Ukraine and has also enforced economic sanctions on Chinese companies over alleged human rights violations in Xinjiang.
China retaliated with tit-for-tat sanctions on US firms, saying the US should "stop interfering in China's internal affairs".
The Taiwan trip would be the latest pressure point in US-China relations, but also an opportunity for Mrs Pelosi to drum up political support back in the US.
Ahead of this year's US mid-term elections, the Democratic Party faces the prospect of losing its majority in the House of Representatives. Mrs Pelosi, 82, may not return as Speaker after the polls.
Earlier last month, her reported plan to visit Taiwan had received bipartisan support in Washington, including from Mr Gingrich himself, with lawmakers from both the Democratic and Republican parties arguing that the leader of the US Congress should not give in to pressure from China.
4. Latest in Mrs Pelosi's China-opposing stances
The House Speaker has a "penchant for high-profile gestures designed to poke China's communist rulers in the eye", says Mr Mike Chinoy, a senior fellow at the University of Southern California's US-China Institute.
She had led American calls for a "diplomatic boycott" of February's Winter Olympics in Beijing over the alleged human rights abuses in Xinjiang.
In 1991, she visited Tiananmen Square, unfurling a banner in remembrance of the deceased demonstrators.
China has branded Mrs Pelosi "full of lies and disinformation" over the Winter Olympics boycott and her trip to Taiwan will worsen tensions, even though some analysts have characterised the visit as "symbol over substance".