Nato has let the US know it can count on its support
Nato's decision to provide the United States with military assistance following Tuesday's terrorist attacks was both unprecedented and hugely symbolic.
Never in the alliance's 52-year history have Nato members invoked Article Five of the Washington treaty, the founding charter of the alliance.
It means, in effect, that the allies agree that they are all in this together.
Wednesday's declaration spelled it out: "Article Five of the treaty stipulates that... each ally will assist the party that has been attacked by taking such action as it deems necessary."
This announcement has already triggered fevered speculation that Nato might be planning a large-scale military intervention in Afghanistan, where the Saudi-born militant Osama Bin Laden is being sheltered.
Such speculation, for the time being at least, is unfounded.
But US President George W Bush does now know that if he decides, as seems likely, to take military action against those involved in the outrages, he can count on alliance support, including access to Nato resources.
Concern
Not every member is happy about this.
Turkey, which already hosts US and UK warplanes involved in patrolling the northern no-fly zone over Iraq, feels that it may be vulnerable if its bases are used for a round of air strikes.
Germany, home to thousands of suspected Islamic militants, is also nervous.
The country's Defence Minister, Rudolf Scharping, has warned against an hysterical response.
"We are not on the brink of war," he said. "We are facing a serious terrorist challenge, and to that there will be an appropriate response."
Calming effect
In the UK, the hope is that widespread international support (including from non-Nato members such as Russia, Japan and Australia) may have the effect of staying Mr Bush's hand - of preventing an instant, intemperate response of the sort being urged by some American politicians.
Almost everyone acknowledges that Washington reserves the right to respond to such a brutal act of war, but the word "proportional" resounds in the corridors of power across the globe.
"With every passing hour, the pendulum swings away from knee-jerk retaliation, towards something more measured," said one senior defence source in London.