I was living in Spain and no one needed the US to explain why they "believed some of Al-Qaeda's associates were in Afghanistan". I'm not sure if you didn't watch the news through that time or what, but the Taliban were very upfront about having Bin Laden.
E.g.: https://www.cbsnews.com/news/taliban-wont-turn-over-bin-lade...
They wanted evidence that Bin Laden had anything to do with the attacks (which of course he denied).
Why not deliberatively and carefully provide this evidence to the world instead of rushing into a war? What's the strategic value there?
"Well, we had thousands of civilian and US military casualties, but we got Bin Laden! It was totally worth it!"
What are you talking about? Bin Laden took credit for 9/11 immediately and it was pretty clear that they had their training camps in Afghanistan. Nobody denied that.
Iraq was a different situation. to go there the US had to make up things.
Both my recollection and Wikipedia (admittedly neither being authoritative) agree that Bin Laden denied involvement for some time after the attacks (Wiki says he didn't claim responsibility until 2004). The Taliban denounced the attacks the day of and, separately, stated Bin Laden wasn't involved (which might seem weird, but there's some background there that makes it less suspicious than it seems, though of course it could have all been deception). They also volunteered that they'd turn him over if we turned up evidence that he'd been involved, on Sept. 13th (again, of course they could have been lying or stalling, just getting the events/statements straight)
The US demand (Sept. 14th) wasn't that they hand over Bin Laden, it was that they hand over all of Al Qaeda in their territory, all their intelligence on them, and Bin Laden. Given that there were a lot of fighters on their side of the civil war who'd been through Al Qaeda camps, this was probably impossible to do without losing the civil war, between the loss of manpower, the risk (I'd hazard it was a near-certainty) of opening a new and dangerously ill-defined front in the civil war, and the loss of said training resources/facilities. It was never going to happen, and we'd been considering covertly or overtly pitching in with the other side of their civil war for a few months prior (that part I didn't know until just a few minutes ago) anyway.
[EDIT] reading over the sequence of events and the public statements of both sides the Taliban comes off as even more reasonable than I remember them seeming at the time, which was already "fairly reasonable". Could have all been lies, of course, but if you just look at the public statements and the timeline of events—how quickly it escalated—just, wow. At the very least it was terrible PR management on the US' part that we came off looking like unhinged lunatics compared with such genuine shitbags as the Taliban.
Do you actually believe this? If so, you are misinformed.
If you do continue to believe this: which misquoted video are you going to trot out for this claim? The 9/16 video? The 9/28 video? Can you tell me which credible Arabic translator regards either (or any) of these as "[taking] credit"?
Nobody seriously continues to maintain that Bin Laden "took credit for 9/11 immediately."
Perhaps you are talking about the November video (although obviously that's not "immediate")? Even if this video does show Bin Laden (which of course is very much disputed), the person in the video doesn't "take credit" in the typical sense of the phrase.
Alternate view: what was to be gained by deliberatively and carefully providing further details on their intelligence sources for general explanations they'd already offered, when it was palpably obvious the Afghan government had no intention of changing the position they'd held for the last three years that there was no way they were going to betray Bin Laden to Libya, never mind the United States? Where was the advantage to engaging in a war of rhetoric with an government committed to protecting somebody that openly called upon his fellow Muslims to bomb the US, a government whose leader compared the notion of giving up Bin Laden to "the end of Islam" and was obviously going to dismiss any evidence presented as insufficient. (even more obvious with the hindsight of what happened a couple of years later when flimsy presentations of evidence harmed the US case for war in Iraq even before it became clear most of the evidence wasn't true)
It's difficult to argue the US action in Afghanistan solved much (though there are certainly people who have benefited as well as those who have suffered as a result) but it's even more difficult to argue they were in a position where they could show that fatwas against the US and series' of attacks culminating in flying jetliners into buildings didn't have any consequences if you weren't a government but had the tacit support of one.