What did they cost us? In addition to the immeasurable cost of about 3,000 lives lost, there were measurable costs as well. We can begin with the loss of several buildings in New York and the damage to the Pentagon that cost millions to repair. We can look at the damage to our economy (from tens to hundreds of billions), the increased cost of security, and all the other things that have changed since 9-11. All of that damage for the cost of about $500,000 and 19 men who wanted to die anyway.

One point of military analysis is the cost of a weapon compared to the cost of what you want to destroy. If an inexpensive weapon (like a Hellfire missile) can take out an expensive one (like a main battle tank), then the weapon is cost effective. For example, an RPG may only cost a few dollars and it can take out lightly armed vehicles or even multi-million dollar helicopters. It's a very cost effective weapon. On the other hand, it wouldn't make much sense to create an expensive weapon that was only capable of taking out inexpensive targets. We have a very powerful military, but it's still hard to find someone hiding underground.

By that measure, terrorist attacks are very cost effective and difficult to stop. Anyone with the proper training can take 100 pounds of explosives and do millions of dollars worth of damage in a single evening. In any town or city, you can easily find plenty of targets.

That leads to the question, why have they not attacked us at home since 9-11? Our security isn't that good compared to the number of targets. It seems unlikely that we've disrupted them that much. Perhaps they're saving up for another big attack - reports indicate that it took several years to put together 9-11.