Conquest from who?

I generally take the word "conquest" to mean some outside force coming in and taking over. That didn't happen in either Vietnam or Korea. You could argue that the USSR used conquest to take over territories for the soviet union. However, that's not something really arguable about Vietnam or Korea. Vietnam, in particular, was the native population overthrowing their conquerors, the french, and then deciding they wanted to be communists. They got support from both the USSR and China, but they weren't ultimately under the umbrella of either regime.

Now, I'd agree that Vietnam and Korea both had civil wars supercharged by the US, China, and Russia. But I disagree that these were wars where the US was stopping conquest. We see that in the modern state of Vietnam and North Korea. Vietnam, funnily, became a closer ally to the US than China after the war.

Cuba is very much the same way. It wasn't conquered by an outside force. Yet they did ally with the USSR once the dust settled. They were still an independent nation from the USSR.