Why are we fighting in Afghanistan?

From The Untold History of the United States By Oliver Stone and Peter Kuznick.

“He explained that the United States and its allies had invaded Afghanistan because it had provided sanctuary for Al-Qaeda which was responsible for 9/11. He forgot to mention at least three crucial facts. First, only fifty to one hundred of Al-Qaeda’s worldwide total of 300 cadre were actually in Afghanistan, while the rest of its badly degraded force operated out of Pakistan and received most of its support from citizens of U.S.-backed regimes in Saudi Arabia, Kuwait, Yemen, and the United Arab Emirates. Second, Taliban leader Mullah Omar had actually opposed the 9/11 attack against U.S. targets. According to the official report of the 9/11 Commission, ‘As final preparations were under way during the summer of 2001, dissent emerged among al Qaeda leaders in Afghanistan over whether to proceed. The Taliban’s chief, Mullah Omar, opposed attacking the United States. Although facing opposition from many of his senior lieutenants, bin Laden effectively overruled their objections, and the attacks went forward.’ And, third, terrorists didn’t need a safe haven replete with training camps to conduct clandestine operations. As Paul Pillar, the former deputy chief of the CIA’s counterterrorism center, pointed out, ‘the operations most important to future terrorist attacks do not need such a home, and few recruits are required for even very deadly terrorism. Consider: The preparations most important to the Sept. 11, 2001, attacks took place not in training camps in Afghanistan but, rather, in apartments in Germany, hotel rooms in Spain and flight schools in the United States.'”

The US has not attacked the countries supporting al-Qaeda nor Germany, Spain or the US flight schools.