“You cannot invade the mainland United States. There would be a rifle behind every blade of grass.” ~Fleet Admiral Isoroku Yamamoto
It will not be necessary to invade the United States, only to place sufficient number of economic sanctions upon us.
The Chinese could come in, argue before our own courts, and win judgments by which they could begin mining the Grand Staircase/Escalante National Monument area of southern Utah for its coal reserves, and expart them directly to China. The same with the known oil reserves under Federal lands, in underwater coastal areas of our East coast, the Gulf, and even off the pristine beaches of Santa Barbara, California.
And we have a Federal judiciary that would fully support them on this.
The Chinese have done their homework well. And they are intent on developing much more sophisticated intelligence efforts than we are now willing to expend.
The Art of War is an ancient Chinese military treatise attributed to Sun Tzu, and one of the provisions is to force the opponent into expending their time, treasure and resources, preferably against a third party, to the point of depletion. Another is to acquire as much intelligence as possible BEFORE a confrontation, and with careful application of this intelligence, force a victory with scarce a shot being fired.