How Al Qaeda has Evolved Since Sept. 11

From Mike Shuster of NPR:

In a message posted on an Islamic website, a group taking responsibility for the London attacks said they were in retaliation for the British "massacres" in Iraq. It also warned Denmark, Italy and "other Crusader states" to withdraw their troops from Iraq and Afghanistan or face similar attacks.

Terrorism experts do not agree on the meaning of these messages. Some say they are disingenuous and that even if the U.S. and its allies change policies or withdraw troops, the attacks will continue. But other experts insist the U.S. needs to understand that its policies in the Middle East and elsewhere elicit a terrorist response and need to be reevaluated.