Reply #10: original reason for invasion....

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The War in Afghanistan, which began on October 7, 2001, was launched by the United States, Canada and the United Kingdom in response to the September 11, 2001 attacks. It was the beginning of the War on Terror. The stated purpose of the invasion was to capture Osama bin Laden, destroy al-Qaeda, and remove the Taliban regime which had provided support and safe harbor to al-Qaeda.

http://en.wikipedia.org/wiki/Afghanistan