I'm a little alarmed at how easily nuclear weapons and using them gets brought up in this thread. And yes, US would send nuke against any country nuking its allies. Let's not get ourselves into hypothetical armageddon kind of scenarios.
Unless China gets significantly more allies in key locations and better nuclear submarines, USN would be able to at minimum cut off ships with Chinese flags headed to the region. Now, it is a good question of how USN, with limited resources, would stop every ship and determine that it is headed to China and not Japan or Korea. I will leave it as that. And as I said earlier, China would be able to also significantly limit the energy and embargo to US if we do get a scenario where they do start attacking civilian trade/energy routes. Life would be suddenly very hard for citizens everywhere. Which is again why I think there will large calls for the two countries to come to a peace agreement once it becomes obvious this is headed into a war of attrition.
The nuclear weapon scenario is useful though in determining ultimate escalation ladder of any conflict between US and China. Depending on the type of attack against the chinese mainland (especially with regards to civilian targets), it would be possible for China to use nuclear weapons in retaliation if china has no other credible defense (although that would be open to interpretation). This is well engrained in discussions at both the government level and with the chinese populace. It is also true that the United States would nuke any country nuking itself or its allies. Therefore for the first step of the analysis, its reasonable to conclude both sides could use nukes.
Second level analysis: Assume that a nuclear exchange between the US and China costs around 500 million chinese lives and 80 million american lives (which would be a reasonable MAD assumption). If the possibility of China retaking taiwan is 50%, what would be the support of this outcome in China vs the US? Even with this lopsided ratio, I would assume the chinese public would have a higher support for this vis-a-vis the US, even if the US comes out with an undoubtedly superior kill ratio. Therefore the US would not want to go all the way through the escalation ladder.
In fact, it would be reasonable to assume that no matter how brutal a conflict between the US and China, the US would likely offer China repeated assurances that it would not attack civilian targets on the mainland, or only with methods for which a credible defense does exist (i.e. cruise missiles vs ballistic missiles) so that China wouldnt go nuclear.
I am also hesitant to quantify the impact of a complete blockade on China by the US. Russia, Pakistan, Mongolia, and Central Asia have no chance of following this, and depending on when this conflict happens (i.e. 2025, 2030...) the risk to China's energy supply chain grow less and less. Yes, China will always need oil through the ocean, but within the next 5 years this demand will be much less or at least fungible, with greater energy generation through renewables like solar, wind, hydro, nuclear and even coal (which is dying but can be turned back on).
Assuming that it took $30 trillion to turn China into the world's first electro-state (an article delves into this in the economist), I would say China has already spent half this amount through investment in EVs, the land portion of BRI, and research into battery density and solid state. Yes, while rare earths do come from Africa and argentina/chile/bolivia, most of china's battery research is now focused on sodium and nickel batteries, the first cost-competitive EVs which already started rolling out across China the past few years. Basically the worst case scenario of a full fledged containment by the US and all western powers has been the
baseline assumption of China's political and economic projections into the 2030's, and anything less than that can already be thought of as
upside.
