Land grabbing.
From PLAs 2003 speech:
"The first issue is living space. This is the biggest focus of the revitalization of the Chinese race. In my last speech, I said that the fight over basic living resources - including land and ocean- is the source of majority of wars in history. (...) Not only our ability to sustain and develop our race, but even it's survival is gravely threatened, to a degree much greater than faced by Germany back then.(...) To solve this problem we must lead the Chinese people outside of China, so that they could develop outside of China"
https://www.trunews.com/stream/chinese-general-pla-must-kill-all-americans-with-biological-weapons
This is the crux of it all. Why would China so aggressively and overtly attack the US and the world?
The world is entering a grand solar minimum. This will affect prosperity world wide. Most noticeably, the food chain. As surplus food production dries up, nations will panic and stop exporting. China will not only lose the food imports they depend on, but they will also lose 30-40% of their own food production. This means losing over half their food supply in the next half decade. If this happens, the leadership will be dragged into the street and slaughtered. It’s an existential crisis for them.
I disagree, they will take their nation to war and march into other nations, stripping them of resources while culling their own soldiers for the cause. Who could stop them without taking the world into a nuclear holocaust? Who else could raise an army large enough to stop them?