Many posts above have alluded to this fact, but I'll repeat it since it may help you in the long run.
Neither of the two American wars being waged in Afghanistan and Iraq are for traditional reasons. There was no threat to the US. This has everything to do with the Military Industrial Complex, and its iron grip on American foreign policy.
The MIC requires war because that's how they sell their products. I would have expected that on a site like HN, this would be obvious. President Eisenhower prophetically warned [1] against the MIC, as he clearly saw how a positive feedback loop would form between private military contractors and US foreign policy, inciting conflict after conflict in order to keep customer demand high for their products.
Although you have obviously been thoroughly steeped in the propaganda offered by these two organizations, who could never acknowledge the truth of their actions, to any rational observer there can be no other justification. The US as a whole has everything to lose, and nothing to gain, by slaughtering defenseless civilians in an impoverished developing country.
Big defense contractors and the politicians they bribe, however, have everything to gain. And they are winning. This is one of the many failures of democracy, one that requires extreme oversight and prosecution. Sadly, we are primates, and we will succumb to our natures sooner or later.
1. http://coursesa.matrix.msu.edu/~hst306/documents/indust.html