I don't think this is realistic. A few thoughts in no particular order:
- War is logistics and you're talking about trying to get involved in a war, that would necessitate supply lines thousands of miles long, between two countries that are separated by 80 miles.
- China is extremely technologically advanced with the largest military in the world, by a wide margin.
- China is the at-scale manufacturing king of the world. In a shift to a war economy, nobody would be able to come even remotely close to competing. They parallel the US in WW2 in a number of ways.
- China is a nuclear power, meaning getting involved is going to be Ukraine style indirect aid to try to avoid direct conflict and nuclear escalation.
- Any attempt to engage in things like sanctions would likely hurt the sanctioners significantly more than China.
- The "rest of the world" you're referring to is the anglosphere, EU, and a few oddballs like Japan or South Korea. This makes up less than 15% of the world, and declining.
- War fatigue is real. The US really wanted to invade Syria, but no matter how hard we beat the war drums, people just weren't down with it. I think this is because people saw major echoes of Iraq at the time, and Taiwan will have a far louder echo of Ukraine. This isn't a show many people will be enthusiastic about rerunning.
I think that, if China tries to take Taiwan, rather than a direct military confrontation, the US might just block the Straits of Malacca against oil heading for China - or maybe against anything heading for China.
China would enforce a blockade against Taiwan. The US might or might not be able to break it. But China would have a very hard time breaking a US blockade down there.
> supply lines thousands of miles long, between two countries that are separated by 80 miles
I think this one is particularly important. IIRC, it's usually phrased something like "if the USA sends aircraft carriers across the pacific, then China has an unsinkable aircraft carrier 80 miles away: the mainland". It's a huge home turf advantage.
The USA seems to have a very low appetite for helping allies against bullies at present too. And no appetite for taking US soldier casualties.
* The US has the largest military logistics system in the world and regularly uses it to fight wars. It's a well exercised muscle.
* Being close to the front lines is as much of a liability as an asset. China's ports and shipbuilding facilities will be bombed out, the US' will not.
* This will be a naval and air war. You can't march troops across the strait, and as we've seen in Ukraine, flying them is a no-go either.
* China hasn't fought a war within the living memory of anyone of fighting age.
* You have a weird way of trying to diminish what represents most of the economic power of the world. Let's also add the Philippines and Vietnam to those "oddballs". China will be alone. And don't forget that China's population is shrinking.
* War fatigue is not an issue here when it comes to Taiwan. Adventurism in Venezuela was emboldening. We'll see what happens with Iran. I live in the generally pacifist part of the US, and I think most folks would demand that we intervene.
The most likely start to hostilities will be if China declares a blockade. Someone in the US will call their bluff - with warships. If China starts shooting, we're in a war. Moral outrage is an (often unfortunate) American trait.