They weren't humiliated in either front; you do not understand warfare even in theory and history.
1. US-led forces liberated South Korea from North Korea in the 1950s (primary objective accomplished). However, China saved North Korea from potential takeover.
2. US-led forces invaded and occupied Vietnam + Cambodia + Laos for over a decade; an achievement in itself. However, this war did not lead to desired outcome due to incompetence of US-backed South Vietnamese regime. So yes, this conflict represent defeat.
In comparison, what did China achieve in Vietnam when it attempted to liberate Cambodia from Vietnamese occupation? Nothing
3. US-led forces have utterly dominated Iraq in wars since 1991. US destroyed a powerful Iraqi army in 1991, toppled Saddam regime in 2003 and carried out Debaathification project while creating a new Iraqi government in 2005 (primary objective accomplished). US also pummeled ISIS to oblivion at a later stage.
Iraqi PMUs cannot remove US from Iraq by force; do not be stupid. US will leave Iraq only if Iraqi parliament will request it to.
4. US-led forces toppled Taliban regime in Afghanistan in 2002 and eradicated Al-Qaeda Network by 2011 (primary objective accomplished).
Taliban resurged in Afghanistan after a major drawdown of US-led forces in 2014 and due to weaknesses of US-backed Afghan government. However, US will not allow a Taliban takeover of Afghanistan; talks are underway to ensure a negotiated resolution of Afghan political future.
Afghanistan benefits from being landlocked and not easy to reform. Never has been.
Now tell me how many wars have (modern) Iran have won? Your war with Iraq was a stalemate at the borders.