Vietnam was a proxy war against the Soviets during the cold war. The soviet union no longer exists and the US does, so in that respect, at least, the US won the cold war.

I'd argue the Vietnam conflict wasn't really won by either side, the US or the Soviets. While the US took heavy losses and had to leave in a hurry, US culture has remained, not the soviet culture. There's McDonalds and Baskin Robins in downtown Hanoi, I mean. In the sense that a war is a cultural takeover, this is a US win.

Though I dislike even talking about a "winner" in a war. Going to war means both sides have already lost. War is mostly just the violence that follows national failures.