U.S. 'occupation' to blame for terrorism, Muslims say

A University of Chicago professor and a Muslim organization linked to the terror organization Hamas are teaming up to proclaim that American occupation of foreign lands is the reason for terrorism.
Word of the cooperation between the Council on America- Islamic Relations and University of Chicago political science professor Robert Pape over his new book, called "Cutting the Fuse: The Explosion of Global Suicide Terrorism and How to Stop It," comes from CAIR.
The organization announced in a news release that the book is a "powerful education tool" to challenge "Islamophobia" and that Pape will speak at CAIR's 16th annual banquet Saturday night.
CAIR cites the Chicago Project on Security and Terrorism's evaluation: "Through a close analysis of suicide campaigns by al-Qaida and in Iraq, Afghanistan, Pakistan, Lebanon, Israel, Chechnya, and Sri Lanka, the authors provide powerful new evidence that, contrary to popular and dangerously mistaken belief, religion alone motivates only a tiny minority of these attacks. Instead, the root cause is foreign military occupation, which triggers secular and religious people to carry out suicide attacks." 
The website said Pape concludes that terrorism is a "response" to "occupation," rather than having anything to do with Islam, which tells its followers to kill "infidels."
What "occupation" caused the 9/11 attacks?