This is a false equivalence. The United States was not trying to “conquer” those countries in the territorial sense that Russia attempted with Ukraine. Those conflicts were limited political or counterinsurgency objectives fought under strict constraints, often without public support, and with no intention of annexation. Comparing that to a conventional invasion aimed at seizing and absorbing a neighbor’s territory is analytically inaccurate.

US did defeat Vietnam, Afghanistan and Iraq. And indirectly Syria by supporting the insurgency (and we had bases in that Country). It is also worth noting that the US and South Vietnam had effectively contained the North by 1973. The Paris Peace Accords ended direct US involvement and the North violated those terms two years later when it launched a full-scale conventional invasion. South Vietnam collapsed only after the US withdrew military support. Same with Afghanistan. Iraq is flourishing without Saddam and without war. It toppled Saddam’s regime in weeks, and the country now has an elected government, functioning institutions, and no US occupation. Whatever its internal challenges, Iraq is not a case where the US attempted and failed to annex territory. It demonstrates that these were limited political interventions, not conquest wars.

I'd also add that the Vietnamese LOVE the US.

Despite what the USA did in its invasion of Vietnam, not because of it.

Vietnamese are trying to not forget their history: https://en.wikipedia.org/wiki/War_Remnants_Museum

(I'm not sure how many Vietnamese actually love USA, vs how many don't... I just want to remind that different people in the same society might hold different opinions, and the sentiment is certainly not monolithic)

I never really looked into it, but it looks like the vast majority of Vietnamese were born after the war so US culture and trade are way more important contributors to opinion. Vietnamese are some of the most pro-US people in the world.

Vietnam had such massive population growth that there are very few people who even remember the war. On the other hand China was pretty much always ingrained into their “national consciousness” as a permanent massive threat.