False, as false as all the other myriad US illegal invasions.
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http://www.alternet.org/story/93473/afghanistan%3A_the_other_illegal_war
Afghanistan: The Other Illegal War
The U.S. invasion of Afghanistan was every bit as illegal as the invasion of Iraq. Why, then, do so many Americans see it as justifiable?
By Marjorie Cohn / AlterNet July 31, 2008
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The invasion of Afghanistan was not legitimate self-defense under article 51 of the charter because the attacks on Sept. 11 were criminal attacks, not "armed attacks" by another country. Afghanistan did not attack the United States. In fact, 15 of the 19 hijackers came from Saudi Arabia. Furthermore, there was not an imminent threat of an armed attack on the United States after Sept. 11, or Bush would not have waited three weeks before initiating his October 2001 bombing campaign. The necessity for self-defense must be "instant, overwhelming, leaving no choice of means, and no moment for deliberation." This classic principle of self-defense in international law has been affirmed by the Nuremberg Tribunal and the U.N. General Assembly.