I think you're pretty close to nailing it. Remember Russia, China, and S. America as the players and read on.
Remember when the US gave money/intel/weapons/training to the mujahadeen (al quida) to fight the russians in Afghanistan in the 80s? (We couldn't fight them head on or it would be WWIII). If Russia got that Afghan/Iraq/Iran pipeline path, they have $8T worth of oil that we don't, and they don't financially collapse like they did.
Late 80s/90s. Stall. We help iraq fight iran, then attack iraq, to stall that oil. Russia has collapsed but China is growing population and work force faster than we predicted.
July 2001. We can no longer stall for that black gold hat trick (3 nations in a row). Afghanistan rejects us and accepts oil pipeline deal from an argentinian firm. Do we want Hugo Chavez' little conglomerate of nations having their oil, startegic position, AND middle east oil? no sir.
9/11 happens conveniently and we have a reason to invade afghans, toss out the taleban nullifying that Argentinan oil deal. Well, we're there already. Might as well take iraq and iran. It's now or never, as US population and UN ain't gonna tolerate this shit more than once.
By 2008 we'll have taken down afghan, iraq, and iran, and maybe syria. We will have long term presence in the region - forever - which means the new puppet govts don't make deals which could compromise security. This coincidentally means no oil bids from RUS, CHI, or S. America.
Is it best for the Americans? yes. I used to hate on it but I understand it now. it's how it has to be. China is going to be a beast to fck with. Is N Korea shooting missiles and lighting nukes (proxy china!) in hopes we'll move there, and won't accomplish the goals of iran/syria? maybe.
If we don't do it, China DEFINITELY finds "WMD" in iraq and iran in a few years. Sucks, but if we want to continue our standard of living, it is the way it has to be (this coming from a former anti-war guy who finally understands the global implications of what we're doing)
