What would the US do if China attacked an ally?

the way it usually works is, the u.s ally provokes China to do an attack. this has happened several times, but nothing ever comes out of it. examples include, viet nam, india, philipines, south korea, japan, etc. China doesnt attack countries, america does.

i do not imagine China might want to be daft adequate to affix N Korea in any attack upon the country. After observing landscape very last evening that's demanding to appreciate why N Korea might want to consider a stupid action that could want to inflame the comfortable challenge that exists. in the journey that they do hit united states of america interests with a missile i believe the country might want to reply in variety and that i think they already have pinpointed aspects that could want to be hit as an instantaneous reaction. N Korea is desperately undesirable and fewer than resourced yet i became surprised at what percentage infantrymen were shown to be marching on Parade.

China's entire manufactioring sector is aimed at U.S. consumers and is entirely dependant on our own consumerism. Nothing necessary to the existance of the United States as a functioning nation-state comes from China.

We would drop the ally faster than a mule drops extra weight. But China wouldn't attack an ally of ours, they are so dependent on the US buying their cheap good and the US selling them grain that they would face a economic collapse. And when the peasants get hungry they blame the leaders, in the US we would cast a vote with a ballot, in china a vote is cast with the bullet.

I think China relies more on US consumers than the US does on Chinese manufacturers. If China attacked a NATO country, it's economy would collapse because they would lose 80% of their markets. The downside to the US is that we lose cheap goods until we begin manufacturing themselves or we find alternate suppliers.

China would loose one of its biggest customers, the UN would condem China and its exports, only Chinas allies would benefit from Chinese exports but they're aren't many, so extreme sactions would be imposed, not only from the US but the UN since Japan and S. Korea are memebers.

It's the US that's been attacking people, not China or Iran.

Obama would dump the ally -

China sells the US stuff not much the other way round so the US is a customer, so Chinese economy is also dependent on the US and they understand that, we don't.

I doubt either economies would totally collapse.

There is no indication that is a possibility let alone a probability.

Paranoia is a dangerous game to play in geopolitics.