It should have ignored the American government, who did as all governments do with anything that happens - see it as a vote-catcher, and act accordingly.
The American government saw a seriously monumentally horrible thing happen, so naturally their response had to be seen by the electorate as proportionate and vengeful - bring on 'The War On Terror".
Of course the term is utterly meaningless, but that's what politicians do, as fast as possible they get a label up and running, and hang everything they do next on that.
What they did was meaningless, counter-productive, and cost billions of dollars and millions of lives to spin military wheels for a few years, and then revert back to where we started from.
What should we have done?
Ignored the knee-jerk political opportunism of Bush, accompanied by the equally pointless and repellent knee-jerk piggy-backing by Blair, and actually thought through a response that didn't involve pretending that invasion was going to solve the problem.
Because the result of that strategy leaves is where we are now - and that is using 20/20 hindsight to see the utter moral bankruptcy of the Bush and Blair governments, and the horror they have created in search of votes.
We should have taken a breath, had a long hard think about what we wanted, work out if we could get it, and what the cost of getting it was going to be.
If we had done that, invasion would not have happened.