Uh...because that's not an alliance?
Perhaps true of the individual perpetrators, but the coordination implies some degree of strategic thinking. I think it's more than revenge and/or hatred.
Uh...because that's not an alliance?
"Is it possible that we don't need allies with whom to have mutual defense pacts..."
Is an alliance merely an agreement for temporary cooperation, or does it involve promises of future action under given conditions? I see a distinct difference between mutual defense pacts, such as NATO -- precisely what George Washington wisely advised against -- and unilateral aid to strengthen nations against perceived adversaries, in return for which the recipients sometimes perform services for us to keep the aid flowing. This isn't even an alliance, IMO, but a series of acts of mutual benefit by and for each. Upon the demise of the perceived adversary or the dissolution of the threat, the nature of the relationship should be re-evaluated.
We are stuck in a cold-war mentality vis-a-vis Israel. Our close relationship might do more harm than good in pursuit of the current adversary (as should have been seen 10 years ago) but could become quite important again at some time in the future.
We shouldn't forget that we created not only Saddam Hussein and Usama bin Laden, but to a great extent the military threat of the Soviet Union which made them seem necessary, and the conditions in Germany (not to mention Japan) which led to Hitler's rise, initially making a militarily strong Soviet Union seen necessary.
How far back should we go to evaluate what got us where we are today? Doing so is not for the purpose of hand-wringing but with the hope it might guide us to avoid similar mistakes in the future.