The US doesn’t officially recognize Taiwan as an independent nation, but is committed legally to sell them arms. A new batch of declassified Reagan-era cables gives some of the most specific insight into how this works in practice.
The US informed China that securing a cut in US arms sales would involve China committing to a peaceful resolution of Taiwan’s status, and that more hostility would mean more arms sales. This appears to be roughly what the US continues to do to this day.
At the same time, the US committed not to change its position on Taiwanese sovereignty, but would continue to make available arms to them. This has left the US with a rather novel position on Taiwan and US-Taiwanese relations.
The US recognized Taiwan’s Kuomintang-dominated government as the Republic of China through 1979. After that, the US recognized the People’s Republic of China (PRC) as China, and has referred to the Kuomintang-occupied island of Formosa as Taiwan.
Maintaining this has been a complicated matter, with the US selling arms to unrecognized Taiwan, and operating the American Institute in Taiwan as a de facto embassy in the country. The US position largely sustains itself by riling up China over Taiwan’s status.
New announced sales to Taiwan always lead to Chinese complaints, and the US interprets those complaints as threats, ensuring that they will sell more arms to Taiwan in the future.
Hey, gotta sell military equipment to as many countries as possible. It’s just business.