Answer:
Step-by-step explanation:
I suppose you should be answering China, but it really isn't true. China was an ally on the American Side during WWII. She kept well over a million Japanese occupied while the war in the Pacific raged on. That's probably why she is on this list.
But then in the Korean War, China was an ally of North Korea. The answer really is that among those countries listed, none were completely free of opposing the United States and her allies.
Even in Vietnam, China was actively supplying the North Vietnamese with weapons which means she was fighting a passive war.
The answer really is none, but I think you are intended to answer China.