Europe
Europe's reluctance to get into military situations might also be traced to the fact that, within the living memory of many Europeans, large portions of the region were pounded into flaming rubble during WWII, something that never happened to the U.S. Think World Trade Center multiplied thousands of times. To say that this has got to result in an attitute change of some kind would be an understatement.
Of course, England has backed us enthusiatically in our current efforts, and they got pounded pretty good too during WWII, so maybe this theory doesn't hold up all that well.