[sofixa]

You're pretty wrong about Vietnam. The US got involved to avoid the communists, the most legitimate entity in Vietnam, the one that fought the Japanese and French and which liberated the country from taking control. If the US doesn't intervene, there is never a South Vietnam.

What you described is roughly how things went down in Korea, so maybe you just confused the two.

US sponsored coups and wars, often in favour of downright terrible people (like Pinochet) weren't for "global border security", but for power, resource and against anything vaguely leftist.