Is it realistic to expect the US to have the capability to block its northern borders? I can't imagine Russia siding with the US in the event of a serious conflict, and even ignoring Kazakhstan and Mongolia (which the US will likely find hard to influence), China and Russia have many miles of shared borders. Russia's oil production is in the same order of magnitude as Saudi Arabia and the US and to my understanding is artificially limited to play nice with OPEC.

I think the more interesting scenario is tech embargoes taking away the "building blocks" (e.g. chips) and stalling their tech production. But China is well aware of their deficiency in this area and they've been pushing hard towards what they call "self-reliance" [1].

As for food, I can't imagine the conflict escalating to such a level of hostility and disregard for human life that the world allows the US to blockade China into starvation.

[1] https://www.bloomberg.com/news/newsletters/2020-10-31/bloomb...

https://www.scmp.com/news/china/diplomacy/article/3012888/ch...