I'll give it a shot, but the sentences will be long.
1) There is a new world order emerging where there are new actors on the international stage; previously only nation states used diplomacy, war, trade as means to achieve their aims, these nation states were acting within a logic pattern, and it was easy to hold one nation responsible for its actions, now there are other players too (terrorist organizations).
2) The new threat comes from groups who have utterly failed to create the material and objective conditions within their own societies sufficient to permit them to construct, out of their own resources, the kind of military organization and weaponry that has constituted every previous kind of threat.
(This is an extremely interesting observation from the author. so I will break the 4 sentence rule and elaborate.
The author makes the comparrisson with a man who wishes to build his own home with his own hands. He must come to grips with the recalcitrant properties of wood and gravity: he must learn to discipline his own activities so that he is in fact able to achieve his end. He will come to see that certain things work and that others don't. He will realize that in order to have A, you must first make sure of B. He will be forced to develop a sense of the realistic.
But all of this is lost on the man who simply pays another man to build his home for him. He is free to imagine his dream house, and to indulge in every kind of fantasy. The proper nature of the material need not concern him - gravity doesn't interest him. He makes the plans out of his head and expects them to be fulfilled at his whim.
The arab nations and the terrorist organizations belong in the second category.)
3) If the existence of a nation state is guaranteed by some external authority - whether by the United Nations or the United States - then it means that one of the chief incentives to a realistic policy, both domestic and foreign, has been removed from play; To see this, think back to the old chaotic world in which the law of the jungle operated: here, if a state pursued a domestic or a foreign policy that was too grossly unrealistic, it would inevitably pay the price for doing so - it would be invaded, or annexed, or partitioned - And this meant that the price of any nation state's survival was the cultivation of a heightened sense of realism.
4) The threat facing us - and one of the greatest ever to threaten mankind - is the collision of this collective fantasy world outlined in 1-3 with the horrendous reality of weapons of mass destruction; previous threats were limited to conventional weapons, and that put a logical roof on the threat; 20 guys in a terrorist organization armed with guns can only do so much damage, 20 guys in a terrorist organization armed with nukes...
Or the cut down version.
1) 9-11 showed that the old rules of war and politics are gone forever.
2) Our enemies are not playing by the same rules of realism that we are.
3) We must change the way we fight from the old theory formed by Clausewiz for it no longer applies (due to 1-2).
4) We must prevent the spreading of wmd's at any cost.