[eesmith]

One problem is that "terrorism" is not well defined.

If you use the definition "untargeted civillian attacks", then that excludes the 9/11 attacks. As I understand it, the targets were: the World Trade center, as a symbol of US economic power, the Pentagon as the center of US military power, and flight 93 was headed towards DC, so perhaps the Capital building or the White House, as an attack on political power.

The goals of those who planned and carried out 9/11 was not simply to strike fear. "Al-Qaeda and bin Laden cited U.S. support of Israel, the presence of U.S. troops in Saudi Arabia, and sanctions against Iraq as motives."