United States of America has worst history with china because of Vietnam and Korea war. The entry of China in the Korean War caused a major change in US policy from minimal support of the Nationalist government in Taiwan to Taiwan as protected by the United States.
Currently taiwan government is protected by US government. Taiwan government itself believed in one china policy and claim their self as real china rulers. But now another party democrat in Taiwan want itself as free country and seeking recognition as independent country of Republic of Taiwan a separate identity apart from China called “Taiwanization”.
PRC don’t want to loose the land of taiwan, therefore they push One China policy which claim taiwan as part of china. In Current situation if America give recognition to taiwan as country he will loose taiwan.
United States of America
American government has never support to PRC government the reason taiwan is still protected by America Itself. Currently taiwan is the ninth largest trading partner of the USA. America is No. 1 country selling arms to the world.since the taiwan relation act signed US has sold $12 billion in weapons to taiwan to oppose china. It also sells $1.83 billion worth of defense weapons to defend itself against china. Although from vietnam war america is protecting taiwan, there is not a treat ally with the US. meaning US has no obligation to defend taiwan in the event of an attack.
What US wants from China
Newly elected US president says US will follow one china policy only when china give some rebate in their trade or give some other benefits to America in trade.