But those wars are typically fought to maintain the US status, to preserve its ability to debase the national currency effectively siphoning wealth from the world economy. Self-preservations comes first. I'm just describing the system.
Now in Iran, the intention was to repeat Venezuela and effect regime change in a hostile country, bolstering America's military status.
Whether these wars have the effect they intend is beside the point; you're asking why they were fought, not whether they resulted in "Mission Accomplished".