On September 11, 2001, the United States suffered shocking terrorist attacks on the World Trade Center in New York and the Pentagon in Washington, D.C. Most agree that the attacks were perpetrated by Osama bin Laden and several of his al Qaeda followers and that these same non-state actors had been behind previous attacks on the U.S.S. Cole and U.S. embassies in Kenya and Tanzania. On October 7, 2001, the United States used massive military force in self-defense against such ongoing processes of armed attack by bin Laden and members of al Qaeda in Afghanistan. At that time, the United States also used massive military force against members of the armed forces of the Taliban regime in Afghanistan. This upgraded an ongoing belligerency between the Taliban and the Northern Alliance and triggered application of the laws of war with respect to U.S. military responses in the Afghan theater of war.
Jordan J. Paust,
War and Enemy Status After 9/11: Attacks on the Laws of War,
Yale J. Int'l L.
Available at: https://digitalcommons.law.yale.edu/yjil/vol28/iss2/5