Istaron, you just aren't going to be able to fully appreciate the horror felt by the American people unless you live here and are a part of this great nation. I get the impression, from your post, that you are not.
We have always thought ourselves impregnable to terrorism. It has been shown in the last couple of years that this is not the case. However, I agree 100% with DragonMage. Even if this happened in Estonia, as you surmise, I would be horrified and calling for justice. You can bet your ass if 20,000+ innocent people were brutally and unknowingly murdered in under 2 hours that the USA would be right there helping Estonia via funds, supplies, humanitarian aid, and military power if requested.
I'm not sure that a mass murder of this magnitude has been seen since WWII...
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Now where did I leave that doughnut?!