A mainland D-Day invasion of China would have several critical elements:
1) Major attacks on the United States ports of Bremerton, Washington and San Diego, to impair the US Pacific Fleet, yet not obviously attacks by China. Possibly a third attack on the east coast.
2) A very large fifth column already in place and prepared to act in Taiwan.
3) A very large flotilla of military and commercial ships able to cross the Taiwan Strait.
4) A massive missile barrage concentrating on airfields and military bases.
5) Occupation of Taiwan’s major cities, which would make the mainland forces almost impossible to dislodge by the US.
The casualty assumption for mainland forces could be as high as 90%, assuming that survival of 10% of their forces would be enough to “win” a beachhead. (A similar assumption was made for the Normandy D-Day).
Every Chinese embassy around the world would go into full diplomatic efforts to proclaim that “China is now reunified, and any attack against any part of it is aggressive war by the United States.”
N.B.: While this would generally be the mainland plan of operations, I do not assert that it would work.
In league with Islamacists ?
I've always believed that China is a "silent partner" on the part of the Islamacists.
Anyone remember the 100,000 assault rifles shipped by China in the 1990s that were intercepted by Customs Agents in the US ?
Don't leave out the control of the Ithsmus of Panama by the Chinese (another gift that keeps on giving, thank you Jimmy Carter).