Why does the DPRK (rightfully) hate America and refuse to cooperate with them after being massively bombed, but Vietnam, who was also massively bombed, now have a fairly decent relationship with them?

To be clear, I'm not making accusations about Vietnam, I was just thinking about it and found it a little strange.

I can think of some fairly plausible reasons, but just because those reasons are plausible doesn't mean they're actually correct, so I was wondering if anybody had a more concrete historical and materialist understanding of the situation.