Firstly, the Taliban were prepared to hand OBL over but Georgie wouldn't have it. Needed a country to bomb the crap out of.
I seem to recall that coming to light as well. The W. Bush administration declined to pursue regime change in Afghanistan as I recall; the second Iraq incursion occurred after the Afghanistan invasion.
The border between Pakistan and Afganistan is almost non existent.
What? Afghanistan shares a long border with Pakistan. The Afghan-Pakistani border is made up of Afghanistan's entire southern border extending to the northwest till the border of China for about less than 200 miles in which Tajikistan border rests at that point. Kyrgyzstan rests to the north of that. If you look at the positioning and regime changes in the region, this places US/NATO and Western friendly regimes to Russia's west and south (it's underbelly) as well as to China's west, south via distant Australia, and east via Taiwan, South Korea, and Japan. 9/11 is inevitably being used to Cold War style contain and isolate Syria, Iran, Russia, and China as well as use military force to sustain the US Dollar as the world's reserve currency and attempt to limit international rivalry (choke points seem to be the principle objective). Inevitably, the narrow border appears to be Afghanistan with China.
Further; Al Quaida was invented by the CIA to drive the Russians out of there. OBL was employed by the CIA to run the secret base and get Islamic extremists to fight for the cause. If you wanted to root out Islamic extremists, then bomb Saudi Arabia flat. That is where the Whahabbis are.
Saudi Arabia and China are becoming increasingly trade partners, and Saudi Arabia is one of the principle drives behind the Pedrodollar system presently sustaining the US Dollar as the world's reserve currency. If the trend continues, the kid gloves the US leadership have granted Saudi Arabia risks coming off. We're definitely in the cusps of an increasingly heated Trade War, and trade wars via sanctions/embargoes tend to be precursors to major conflict.
Don't start about "Bringing Democracy" to Iraq, my friend, you can not bring democracy at the muzzle of a machine gun.
Nothing really comes out of forcefully installing one's idealistic, ideological, form of governance, and etc to another but conflict.