How does the idea of communism threaten capitalism?

I just learned this. Communists wanted to spread communism. And russias army was scary. USA was like screw that, we're not going to bow to anybody. NUKES. But Russia responds quickly, and because they have a single party communist government at the time which pretty much means no elections, they have exellent spys. So Russia discovers the nuke tech. from the USA then the cold war is on. Not helped by the cultural revolution in China; USA backed the side that lost. Basically the communists won.