You lost me at step 1. Why would we get in a war with China? Again it benefits absolutely no one. China is watching as the US shoots itself in the foot daily and we are no longer a global leader. I mean they’re talking about rolling back mileage ratings for fucks sake. Gasoline is expensive as ever and they want to bring back cars that measure mileage in telephone poles?
Quoted against the wanna-censor status, and even though the visibility is still high?
Anyway, the most answer to your question is Taiwan (per other replies), except I'm adding a proviso that I think the Chinese are too smart to start any warlike situation unless they are sure they have already won it. (There are some less obvious answers, but as far as I can imagine (right now and based on limited data) the risk-benefit ratios are too low for all of them.)
Having said that, I'm pretty sure the Chinese tactics would involve clouds of cheap drones and minimal actual attacks. I think it most likely that they would declare an embargo-not-embargo and merely require each ship going to or from Taiwan to visit China for complete inspection of the cargo. Certain things will get blocked or delayed, but they will do it in such a capricious way that it will be difficult to justify any interventions from outside, while the actual higher level strategy will basically be economic. After all they don't want to destroy the Taiwanese economy, but they will, if push comes to shove, seek to maximize interdependence-really-dependence with some kind of seasoning of threat control.
The Subject has become kind of confusing or even misleading, but still relevant, though I think for AI more than cars. I guess it depends on how much manufacturing goes to the robots?