Columbia subject headings:
September 11 Terrorist Attacks, 2001--Causes.
September 11 Terrorist Attacks, 2001--Influence.
United States--Foreign relations--2001-2009.
Harvard subject headings:
September 11 Terrorist Attacks, 2001--Causes.
September 11 Terrorist Attacks, 2001--Influence
United States--Foreign relations--2001-2009.
Princeton subject headings: