I believe the rest of the world is suprised something like this did not happen sooner.
For quite some time now international opinion (including allied nations) has been swinging against the US.
Your average world citizen sees the US as egocentric, decedent hiprocrites whos government and industry are completely driven by popular opinion and greed all not-so-cleverly passed off under the guise of objective ethics.
I dont condone any terroist actions, and the loss of life is appalling. However the rest of the world will judge very harshly if the US acts in a blind retaliatory witch hunt.