Here is the real reason for the US invasion of Afghanistan. It’s not about 9/11. It’s not about punishing Osama bin Laden (for who knows which particular Saudi terrorist group had actually attacked the Twin Towers), though it would be great for President Bush had Osama been nabbed and brought back to the USA for trial. It's not about retribution for those victimised in 9/11 though it did serve to show the American people their president was "strong" in punishing those who dared to touch the USA (doesn't matter whether the correct party has been punished).
The oil pipeline from the oil-rich “-stan” countries of Central Asia to the Indian Ocean via Afghanistan was an old pipe dream that became a deal between the USA and its old ally, the Talibans. Piping oil from the Central Asian countries to the coast of the Indian Ocean through Afghanistan would have allowed the Americans to avoid transiting the precious commodity through either Chinese or Russian territories.
But things went sour when their erstwhile ally the Talibans cancelled the deal in the latter's decision to close the Afghan’s door to the world and retreat into their own conceived splendours and magnificence of a medieval Islamic State.
The Americans were naturally peeved, as the slamming shut of the Afghan route left open only the undesirable alternative of taking the pipeline east through China, God forbid, or west through Russia, definitely not.
When 9/11 occurred, the excuse or opportunity to resurrect that pipeline through Afghanistan made itself available again. An invasion and occupation of the backward nation and the subsequent installation of a former UNOCAL employee as Afghanistan president would make facilitate the building and maintenance of the pipeline nicely. Read this about Ahmad Karzai and his connection with UNOCAL and the Americans.
Just like Iraq, Afghanistan was about oil. Osama bin Laden was just the excuse.
9/11 – Sex, Lies & Videotape