I look at it more in terms of concrete, material support: if you're geographically near a Communist state, that Communist state has a strong interest in undermi

I look at it more in terms of concrete, material support: if you're geographically near a Communist state, that Communist state has a strong interest in undermining your government for its own ends. It's also far easier for them to supply material and men, rely on social networks to diffuse propaganda, etc. A Communist Vietnam IMO makes a Communist Indonesia and even India much more likely (which would be a disaster on a huge scale); South Africa or Peru, though, next to no effect, or maybe even a negative effect. The real genius of Kissinger was realizing the abstraction of a unified Communist block was pretty faulty, and national interests superseded any ideological fidelity to the Communist cause.