"I am clear on my answer: I will not repeat the mistakes were made in the past---the mistakes of staying indefinitely in a conflict that is not in the national interest of the United States, or doubling down on a civil war in a foreign country, of attempting to remake a country through the endless military deployments of the U.S. forces. those are the mistakes we cannot continue to repeat, because we have significant vital interests in the world that we cannot afford to ignore."

The above-mentioned remarks, which can be found in the official website of White House, are made by U.S. President Biden after his government decided to withdraw from Afghanistan all American troops and diplomats.  The part highlighted in red clearly indicates the U.S. does not intend to interfere in a civil war in a foreign country any more.

Brainwashed people of Taiwan, especially those naive youngsters, may think Taiwan is a "country", so any war that might be taken place across the Strait is an "invasion" from China, and Americans (or even Japs) may come to help the island out.  The fact is the status quo across the strait has be an unfinished civil war between PRC and ROC, and now both sides are just in the state of truce without even signing a peace treaty.  There is only one de jere China, so in case the war breaks out again, it is merely the continuation of the civil war, and it will only end when either one reunite the whole China again.    

These days, due to that shocking "fall" of Afghanistan, the issue of a sustainable peace across the strait has been brought up again.  Needless to say, signing a peace treaty with each other for both sides is the first step.  There must be a political settlement to meet the One China priciple in that treaty; otherwise, the only way for people of Taiwan is to keep on living in the days of "little positive happiness" till the doomsday comes.

Always remember this: Taiwan may be one of the national interest of the U.S., as President Biden may think it is; but it is definitely the core national interest of China Mainland.