Yeah true, but producing enough basic calories to feed their own population will never be a problem for the US. And they are engaging in protectionism. As long as the US doesn’t disintegrate into civil war, this advantage of their geographic location and size remains.
Heatwaves have already resulted in massive crop loss in 2021. Over 21 billion in crop losses was recorded both in 2022 and in 2023. Meanwhile, soil erosion makes the problem even worse, and scientists are already warning that it is threatening food security. I encourage you to read up on the dust bowl to see where this is all going.
Incidentally, here's a good overview of where farming situation is headed https://lemmygrad.ml/post/5633916/5068182
So yeah the best strategy for China is to remain friendly and non-aggressive and maintain minimal economic stability for their neighbors. And try to increase economic and social instability and dependence in the US. But you see how the US is poking the bear and now china, they want the instability. And Europe, Russia, China and India at each others throats.
The actual best strategy for China is to make friends with Russia who can guarantee supply of resources that China needs and to focus on developing Eurasia with projects like BRI which is precisely what China is doing. In parallel, China will continue to decouple from the US and western economies. This process is already well under way.
I don’t know about Mexico, but there are studies that large parts of India could become literally uninhabitable with too high wet bulb temperatures. After that you can image the talk about “Living space in the north” in Siberia. Plus many other places and large cities near the rising oceans. How can there not be endless conflict spilling out and through the many porous borders.
That may happen, however that's not going to lead to the climate wars you imagine. Once such an event happens, people will simply die out. They will have no time or the means to migrate anywhere. It's also worth noting that US is quite vulnerable to climate disasters as well. The problems of droughts, large scale natural disasters like megafires, hurricanes, and floodings, all apply to US.
It’s painful to consider, but I don’t see the US “loosing” except for civil war or nuclear war. They will have massive problems but they just have to loose less quickly than the rest of the world.
Civil war is the most likely scenario for the US in the coming years. It will be fuelled by the collapsing standard of living, natural disasters, lack of social cohesion. This process has already started and it's very likely irreversible.