Wars the US waged in Iraq, Afghanistan, Syria, Yemen, and Pakistan following September 11, 2001 caused at least 4.5 million deaths and displaced 38 to 60 million people, with 7.6 million children starving today, according to studies by Brown University.
The Taliban were willing (after a bit of threatening and cajoling) to hand Osama bin Laden over to a third party for him to go to trial. There was no need to invade based on the justification as the Taliban were genuinely afraid of the invasion and were willing to co-operate, just as they have been now. In the end, the invasion did nothing anyway and Al Qaeda’s peak came AFTER the Taliban was toppled. There was never any chance of a cohesive post-Taliban government emerging from the Northern Alliance. By this point the US had decided on war and the whole MIC machinery was rolling, so it was too late to turn back (as US leaders thought, with their reliance on a captured media and lobbying from the MIC creating strategic liabilities within the US state).
The invasion was not necessary for US security aims and certainly could never have bettered Afghanistan, though.
did they already plan to use afghanistan to export muslim extremism into xinjiang when they planned the invasion, or did they come up with that idea later?
I think they already had been, Uigyurs were fighting in the Soviet-Afghan war on the side of the muhajadeen and then brought that violence home in the 90s
CIA was heavily involved in creating the Afghan war though, Afghanistan would look like Vietnam or Cuba today if not for that.
I remember reading something about this in the final 9/11 investigative report.