Ruled by separate governments since end of Chinese civil war in 1949
China considers the island part of its territory
China has offered a "one country, two systems" solution, like Hong Kong
Most people in Taiwan support status quo
China's state media has accused the United States of "arrogance" and "double standards" in pursuing arms sales to Taiwan.The state-run China Daily and the Global Times also warned that China's threats of retaliation were real.
The Obama administration approved the $6.4bn arms sale to Taiwan last week.
China has warned of "serious harm" to relations between the two powers, the suspension of military contact, and sanctions on the US companies involved.
'Cold war thinking'
The US has said it will go ahead with the sale anyway, despite China's view that Taiwan is part of its territory.
China's state media said Mr Obama must have been "insincere" when he earlier promised not to "contain" China.
"China's response, no matter how vehement, is justified," the China Daily said, adding the US move "exposes the US's usage of double standards and hypocrisy on major issues related to China's core interests".
"Washington's arrogance also reflects the stark reality of how a nation's interests could be trampled upon by another," it said.
Despite Beijing's insistence that sanctions are not the way to control Iran's nuclear ambitions, the Global Times said in reference to the US-Taiwan deal that sanctions "can be an effective alternative to other hard line measures to deal with a diplomatic dispute".
"It's time the US was made to feel the heat for the continuing arms sales to Taiwan," said the newspaper, which is run by the People's Daily, the Communist Party's propaganda mouthpiece.
"It would be folly to underestimate Chinese unity over the Taiwan question. Punishing companies that sell weapons to Taiwan is a move that would be supported by most Chinese," it said.
Communist Party mouthpiece the People's Daily said in a commentary that the arms sales showed Washington's "rude and unreasonable Cold War thinking".
"When it comes down to it, the United States is still drawing lines based on ideology and coming up with a million ways to stymie China's development and progress," the paper's overseas edition said.
"If the United States stubbornly persists in this Cold War thinking and ignores China's core interests and grave concerns, the United States will further damage the development of bilateral ties and the great task of world peace. In the end, it will reap what it has sown."
In an official diplomatic protest, China said the row would endanger cooperation with the United States on "key international and regional issues."
Beijing has hundreds of missiles pointed at Taiwan and has threatened to use force to bring it under its control if it moved towards formal independence.
Defence ties between Washington and Beijing have been on ice for several years because of differences over Taiwan, though the two countries' leaders pledged to improve them in 2009.
The United States switched diplomatic recognition from Taipei to Beijing in 1979, recognising "one China".
But it remains Taiwan's biggest ally and is obliged by the 1979 Taiwan Relations Act to help in the island's defence.
The US State Department said on Saturday that the sale contributed to "security and stability" between Taiwan and China.
Ties between the US and China are already strained by rows over trade and internet censorship.
by:Ahmad Danial Kahar