China received 2 nuclear threats: USA (1950s), USSR(1960s-1970s).
USA threated the nuclear hit as they were tired of blood shed in korea! As Chinese close ally, USSR's nulcear force was the reason they didn't do it!
In 1969, when China & USSR had the little conflict for the little island, USSR once planned to completely destroy Chinese military ability with nuclear hit! Ironically, this time USA was the one protected China. They warned russians that they would get in if there was a nuclear war! But russian nuclear threat always overshaddow China in the whole 70s. That is the exactlly why Chinese general told Mao:we may loose 300-600 millions people in nuclear war! China was hopeless in a possible sino-russia nuclear war!