An intriguing, short analysis using the START Global Terrorism Database (GTD):
First, the tremendous impact of 9/11 encourages us to think about terrorism as being mostly about dissatisfied individuals from one country attacking innocent civilians from another country. Based on the data in the GTD we found that more than 90% of the 17,000 attacks carried out by 52 foreign terrorist groups were actually domestic attacks.

Second...it is easy to lose sight of the fact that a large number of terrorist attacks involve fairly rational political disputes over territory.

Third...we find that more than half of all terrorist attacks since 1970 involved no fatalities.

Fourth...the vast majority of terrorist attacks rely on unsophisticated, readily accessible weapons.

And finally, the advance planning, originality and destructiveness of 9/11 contributed to the notion that terrorist groups are infallible.
Link:http://forumblog.org/2013/07/top-fiv...out-terrorism/