1. Preventing the US from keeping a significant troop presence in Iraq which it could use to attack Iran in future.
2. Preventing a US friendly regime that could threaten Iran directly (like Saddam) from being planted in Iraq.
3. Making Iraq enough of a nightmare for the US that it wouldn't try the same against Iran.
All succeeded with little resources expended, compared to the trillions the US spent.
Squaring up to the US? Why, there's no need. We just turn Iraq into a multi-trillion dollar quagmire for them and watch them retreat
Yes I'm fucking serious, you constantly use lies to forward your argument. In what fucking universe does causing 25% of your enemy's casualties have no bearing on that enemy's decision to withdraw? You're telling me 1100 dead US soldiers at the hand of Iran - the US Ambassador to Iraq's numbers, not "IRI BS" didn't factor into the US' calculations at all!
Or as an earlier example one of your first acts on this forum was to say that Iran was so incompetent that it had not launched a satellite into orbit when in fact it had launched several, according to NASA and not the "IRI BS" you love to mention.
Though in fairness, it's possible none of these are lies and you are in fact that stupid.