I was speaking of conventional warfare - which is what it would take for a “third front” to be necessary. There’s a huge difference between the assorted military operations we’ve seen in my lifetime and total warfare. Even in Vietnam, the major powers held back. The USA hasn’t actually declared war on a country since 1942.

If the USA actually decides to go all-in on a country, that country is in for a bad time. Even if that country is China. That said, **any **nation that invades China is also in for a bad time. The very idea of such a war is horrendous.