The Soviet Union was in many ways a theocracy, belief in communism being required and other faiths suppressed. And like many faiths it had missionaries all over the world, preaching the Marx/Lenin gospel.
The US considered the USSR dangerous. The successor state Russia is smaller, not evangelical, and we consider it troublesome but do not fear it.
Today's China is supposedly communist but doesn't work very hard at selling its ideology outside its own boundaries. I suspect they believe non-Chinese are too dumb to understand their system's merits.
However, China has a huge population and a rapidly expanding military. We now consider it dangerous and potentially fearsome.
The evangelical faith endangering us today is militant Islam. It wins some converts, feels free to kill those who won't, and scatters its adherents all over the world. Not precisely an existential societal threat, more of an infestation like fire ants or poison ivy, something to keep out of our society.
Later ... it seems Glenn Beaton of Aspen Beat fame has been thinking about this same set of issues. His treatment is more eloquent but his conclusions don't differ markedly from mine. He perhaps admires China more than I do, but his view of Islam seems right. Hat tip to Lucianne.com for the link.